Seismic Design With Base Isolation

Seismic Isolation for Designers and Structural Engineers

This book provides both theory and design aspects of seismic isolation. This will be useful for structural engineers and teachers of engineering courses. For other structural components (concrete frames, steel braces etc) the. engineering student is taught the theory (lateral loads, bending moments) but then also the design (how to select sizes, detail reinforcing, bolts). This book will do the same for seismic engineering. The book provides practical examples of computer applications as well as device design examples so that the. structural engineer is able to do a preliminary design that wont specify impossible constraints. The book also addresses the steps that need to be taken to ensure the design is code-compliant.

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203 Seismic Design Philosophies 2031 Design Evolution

Seismic bridge design has been improving and advancing, based on research findings and lessons learned from past earthquakes. In the United States, prior to the 1971 San Fernando Earthquake, the seismic design of highway bridges was partially based on lateral force requirements for buildings. Lateral loads were considered as levels of 2 to 6 of dead loads. In 1973, California Department of Transportation (Caltrans) developed new seismic design criteria (SDC) related to site, seismic response of the soils at the site, and dynamic characteristics of bridges. The American Association of State Highway and Transportation Officials (AASHTO) modified the Caltrans 1973 Provisions slightly and adopted Interim Specifications. Applied Technology Council (ATC) developed guidelines ATC-6 19 for seismic design of bridges in 1981. AASHTO adopted ATC-6 as the Guide Specifications in 1983 and in 1991 incorporated it into the Standard Specifications for Highway Bridges 20 . FHWA updated its Seismic...

94 Equivalent Static Forces For Seismic Design

The seismic design shear V depends on regional seismicity (Fig. 9.6), which is quantified by a zone factor Z, which approximates an effective peak ground acceleration (on firms soil for the region). Z 0.075 for zone 1 in Fig. 9.6, 0.15 for zone 2, 0.30 for zone 3, and 0.40 for zone 4. Seismic zone 2 is divided into two regions (2A and 2B) which have the same design base shear, but different detailing requirements. The coefficient R in Eq. (9.5) reduces the seismic design forces in recognition of the ductility achieved by the structural system during a major earthquake. A measure of the ductility and inelastic behavior of the structure, R ranges from 2.2 to 8.5. The largest values of R are used for ductile structural systems that can dissipate large amounts of energy and can sustain large inelastic deformations. The smallest values are intended to assure nearly elastic behavior when the overstrength normally achieved in design is considered. Special steel moment resisting frames have...

209 Seismic Design Practice in Japan 2091 Introduction

Seismic design methods for highway bridges in Japan have been developed and improved based on the lessons learned from the various past bitter experiences after the Kanto Earthquake (M7.9) in 1923. By introducing various provisions such as soil liquefaction considerations and unseating prevention devices to prevent bridges from serious damage, only a few highway bridges suffered complete collapse of superstructures in the recent past earthquakes. However, the Hyogo-ken-Nanbu (Kobe) Earthquake (M7.3) of January 17, 1995, caused destructive damage to highway bridges. Collapse and near-collapse of superstructures occurred at nine sites and other destructive damages occurred at 16 sites 71,72 . The earthquake revealed that there were a number of critical design issues that should be reevaluated and revised in the seismic design and seismic strengthening of bridges. 1995, and the Ministry of Construction adopted on the same day that the reconstruction and repair of highway bridges that...

20612 Seismic Design and Analysis Procedures SDAP

For low seismicity areas, only minimum seat widths and connection design forces for bearings and minimum shear reinforcement in concrete columns and piles in the seismic design requirement (SDR) 2 are deemed necessary for the life safety performance objective. The primary purpose is to ensure that the connections between the superstructure and its supporting substructures remain intact during the design earthquake. SDAP A1 and A2 require that the horizontal design connection forces in the restrained directions shall not be taken to be less than 0.1 and 0.25 times the vertical reactions due to tributary permanent loads and assumed existing live loads, respectively. Seismic design and analysis procedure (SDAP) and seismic design requirements (SDR)

Process PerformanceBased Seismic Design

Earthquakes provide architects, engineers, constructors and enforcers with a number of important considerations foreign to the non-seismic design and construction process. As some of these criteria are fundamental in determining the form of the 'structure', it is crucial that adequate attention is given to earthquake considerations at the correct stages in the process. To this end, a simplified flowchart of the design and construction process for earthquake resistant infrastructure is shown in Figure 8.1.

2093Basic Principles of Seismic Design

Table 20.15 shows the performance matrix including the design earthquake ground motion and the seismic performance level (SPL) provided in the JRA Seismic Design Specifications. The two-level ground motions are the moderate ground motions induced in the earthquakes with high probability to occur (Level 1 earthquake) and the intensive ground motions induced in the earthquakes with low probability to occur (Level 2 earthquake).

95 Seismic Retrofitting of Historical Masonry in the United States

The preceding sections ofthis chapter have dealt primarily with the seismic performance ofmasonry built under the reinforced masonry provisions that were introduced in the western United States as part of the reaction to the 1933 Long Beach Earthquake. Such masonry generally behaves well. Unreinforced masonry, in contrast, often collapses or experiences heavy damage. This is true whether the masonry was built in the western United States prior to 1933 or in other places either before or after 1933. As a result of this observed poor behavior, recent decades have witnessed significant interest in the seismic retrofitting of historical masonry in the United States. In this section, those retrofitting efforts are briefly reviewed. Over the past 15 years, efforts have focused on the seismic response and retrofitting of existing URM buildings. The goals of seismic retrofitting are The most basic elements of seismic retrofitting involve bracing parapets to roofs and connecting floor...

96 Structural Steel Systems For Seismic Design

Since seismic loading is an inertial loading, the forces are dependent on the dynamic characteristics of the acceleration record and the structure. Seismic design codes use a response spectrum as shown in Fig. 9.7 to model these dynamic characteristics. These forces are usually reduced in accordance with the ductility of the structure. This reduction is accomplished by the R factor in the static-force method, and the reduction may be quite large (Art. 9.5). The designer must ensure that the structure is capable of developing the required ductility, as it is well-known that the available ductility varies with different structural systems. Therefore, the structural engineer must ensure that the structural system selected for a given application is capable of achieving the ductility required for the R value used in the design. The engineer also must complete the details of the design of members and connections so that the structure lives up to these expectations. While some steel...

1954 Seismic Design Categories

The seismicity of the United States, and indeed the world, varies widely. It encompasses zones of very high seismicity in which highly destructive levels of ground shaking are anticipated to occur every 50 to 100 years and zones of much lower seismicity in which only moderate levels of ground shaking are ever anticipated. The NEHRP Provisions recognize that it is neither technically necessary nor economically appropriate to require the same levels of seismic protection for all buildings across these various regions of seismicity. Instead, the NEHRP Provisions assign each structure to a seismic design category (SDC) based on the level of seismicity at the building site, as represented by mapped shaking parameters, and the SUG. Six SDCs, labeled A through F, are defined. SDC A represents the least severe seismic design condition and includes structures of ordinary occupancy located on sites anticipated to experience only very limited levels of ground shaking. SDC F represents the most...

853 Seismic isolation using flexible bearings

The most commonly used method of introducing the added flexibility for seismic isolation is to seat the item concerned on either rubber or sliding bearings. The energy dissipators (dampers) that must be provided may come in various forms. For use with standard bridge-type bearings made of rubber or sliding plates, any of the energy dissipators mentioned in Section 8.5.6 may be suitable. In addition, all-in-one devices, incorporating both isolation and damping, are used, namely lead-rubber and high damping rubber bearings. The most effective device, the lead-rubber bearing, is discussed below. The lead-rubber bearing (Robinson and Tucker, 1977) is conceptually and practically a very attractive device for seismic isolation, as it combines all of the required design features of flexibility and deflection control into a single component. As shown in Figure 8.12, it is similar to the laminated steel and rubber bearings used for temperature effects on bridges, but with the addition of a...

211 Some Issues in Current Seismic Design

The first question that comes to mind when introducing a new methodology is the obvious one why do we need a new procedure What is inherently wrong or inadequate in the existing provisions for design that warrants a new look at the entire process Hence, the task of introducing PBSE is more easily accomplished by highlighting the limitations and drawbacks of existing seismic design procedures. Since the early development of seismic design codes, global response modification factors (or R-factors) have remained at the core of seismic force formulas. The main purpose of the force-reduction factors used in seismic design is to simplify the analysis process so that elastic methods can be used to approximately predict the expected inelastic demands in a structure subjected to the design loads. They account for reductions in seismic force values due to a variety of factors including system inherent ductility, overstrength, and redundancy. Of these, only the ductility component of the...

30143 Seismic Design

Outlined in this section, are general Seismic design requirements for Ohio. Ohio is considered to be in Zone A based on acceleration coefficients below 0.09. The following information is only meant to highlight AASHTO requirements. The designer should refer to AASHTO for complete requirements.

12 Earthquake Risk and Hazard

Fortunately, an authoritative attempt has been made to overcome this difficulty through the publication by the Earthquake Engineering Research Institute's glossary of standard terms for use in this subject (EERI Committee on Seismic Risk, 1984). Their terminology will be used in this book.

821 Function cost and reliability

The basic principle of any design is that the product should meet the owner's requirements, in a process which since the 1990s has become referred to as Performance Based Seismic Design, or Performance Based Earthquake Engineering. The owner's requirements may be reduced to just three criteria, i.e.

93 Seismic Loads In Model Codes

The Uniform Building Code'' (UBC) of the International Conference of Building Officials has been the primary source of seismic design provisions for the United States. It adopts provisions based on recommendations of the Structural Engineers Association of California (SEAOC). The UBC and SEAOC define design forces and establish detailed requirements for seismic design of many structural types. Another model code is the National Earthquake Hazard Reduction Program (NEHRP) Recommended Provisions for the Development of Seismic Regulations for New Buildings,'' of the Building Seismic Safety Council (BSSC), Federal Emergency Management Agency (FEMA), Washington, D.C. There have historically been considerable similarities between the UBC and NEHRP recommendations, since the rationale is similar for both documents and many engineers participate in the development of both documents. However, there have also been differences in the detailed approach used by the UBC and NEHRP provisions, and in...

1018 Shock Resistant Structures

Accounts of earthquake-resistant design are given in Fundamentals of Earthquake Engineering (Newmark and Rosenblueth, 1971) and Earthquake Resistant Design (Dowrick, 1977, 1987) and by Alderson (1982 SRD R246). UK conditions are treated in Earthquake Engineering in Britain by the Institution of Civil Engineers (ICE, 1985) and by Alderson. Earthquake-resistant design requirements relevant to plant are most advanced in the nuclear industry. In the USA the Nuclear Regulatory Commission requires earthquake-resistant design. It has issued standard earthquake profiles for seismic design and it has had an extensive programme for the seismic qualification of plant. The earthquake-resistant design of major hazard plants in the UK has been investigated by Alderson (1982 SRD R 246). Essentially, he proposes that the approach adopted should follow broadly that adopted in the UK nuclear industry. Some US codes for process plant contain seismic design requirements. An example is NFPA 59A 1990 for...

Note That Top Flange And Coverplate Are Welded Similar To Bottom Flange

Area, well before large stresses develop at the welded connection. This alternative has also performed well, but testing is in progress to evaluate the effects of composite slabs and the lateral-torsional stability of the reduced section. These and other alternatives are discussed in the FEMA 267 documents, and partial design procedures are provided there. At the end of the SAC Steel Project, a number of different steel frame connections will likely be pre-qualified for use in seismic design by structural engineers. These will clearly include a number of different bolted connections as well as welded connections. However a study of these connections is incomplete and the design procedures for the connections are not fully developed. As a result, the structural engineer must currently rely on the experimental evaluation requirements of the seismic design specification. Ordinary Moment Frames. Some steel moment-resisting frames, known as ordinary moment frames, are not designed to...

1111 Detailing For Earthquakes

The Standard Specifications for Seismic Design of Highway Bridges'' of the American Association of State Highway and Transportation Officials contain standards for seismic design that are comprehensive in nature and embody several concepts that are significant departures from previous design provisions. They are based on the observed performance of bridges during past earthquakes and on recent research. The specifications include an extensive commentary that documents the basis for the standards and an example illustrating their use. LRFD specifications include seismic design as part of the Extreme Event Limit State. Retrofitting existing structures to provide earthquake resistance is also an important consideration for critical bridges. Guidance is provided in ''Seismic Retrofitting Guidelines for Highway Bridges,'' Federal Highway Administration (FHWA) Report No. RD-83 007, and ''Seismic Design and Retrofit Manual for Highway Bridges,'' FHWA Report No. IP-87-6, Federal Highway...

982 Nonlinear Analysis of Structural Frames

Although nonlinear analysis is not commonly used for structural design, it is important for seismic design for several reasons. First, while the seismic-design provisions of various building codes rely on linear-elastic concepts, they are based on inelastic response. Seismic behavior of structures during major earthquakes depends on nonlinear material behavior caused by yielding of steel and cracking of concrete. The reduced stiffness due to yielding makes the stability of structures of great concern, and ensuring stability requires consideration of geometric nonlinearities. Nonlinear analysis permits treatment of these stability effects with P - A moments (Fig. 9.21).

2032NoCollapse Based Design

The basic design philosophy is to prevent bridges from collapsing during severe earthquakes 24-27,35-37 that have only a small probability of occurring during the useful life of the bridge. To prevent collapse, two alternative approaches are commonly used in design. The first is a conventional force-based approach where the adjustment factor Z for ductility and risk assessment 21 , or the response modification factor R 20,37 , is applied to elastic member forces obtained from a response spectra analysis or an equivalent static analysis. The second approach is a more recent displacement-based approach 24,35 where displacements are a major consideration in design. For more detailed information, references can be made to comprehensive discussions in Seismic Design and Retrofit of Bridges by Prietley et al. 16 , Bridge Engineering Handbook by Chen and Duan 39 , and Refs 40,41 .

97 Seismicdesign Limitations On Steel Frames

A wide range of special seismic design requirements are specified for steel frames to ensure that they achieve the ductility and behavior required for the structural system and the design forces used for the system. Use of systems with poor or uncertain seismic performance is restricted or prohibited for some applications. Most of these requirements are specified in the Seismic Provisions for Structural Steel Buildings'' of the AISC. These provisions are either adopted by reference or they are directly incorporated into the UBC and NEHRP provisions. However, UBC also includes supplemental provisions and clarifications which supplement the AISC provisions. This article will provide a summary of the provisions for moment-resisting frames, concentrically braced frames and eccentrically braced frames for seismic applications. It should be noted that the 1992 AISC seismic provisions are directly

321 360 3115 384 3105 3114 381

Advantages of steel in conservative dynamic equilibrium of dynamic-load response of local yielding of in earthquakes lumped-mass model of nonredundant load-path redundant load-path seismic design of serviceability requirements for statically determinate statically indeterminate structural integrity in supports for vibration frequency of vibration of vibration period of

846 Hybrid structural systems

While hybrid systems are often unavoidable and can provide good seismic resistance, care must be taken to ensure that the structural behaviour is correctly modelled in the analysis. Interaction between the different components can be large, and is not necessarily obvious, and many papers have been written on this subject. For example, for low-rise buildings it may be reasonable in many cases to assume that the walls or the braced bays resist the entire horizontal earthquake load, and the moment-resisting frame is not required to resist horizontal earthquake forces. However, deformations are still imposed on the moment-resisting members which require some seismic design consideration such as detailing for ductility.

2094Ground Motion and Seismic Performance Level

The seismic design of bridges is according to the performance matrix as shown in Table 20.15. The bridges are categorized into two groups depending on their importance standard bridges (Type-A bridges) and important bridges (Type-B bridges). The SPL depends on the importance of bridges. For the moderate ground motions induced in the earthquakes with high probability of occurrence, both A and B bridges shall behave in an elastic manner essentially without structural damage (SPL 1). For the intensive ground motions induced in the earthquakes with low probability of occurrence, the Type-A bridges shall prevent critical failure (SPL 3), while the Type-B bridges shall perform with limited damage (SPL 2).

20952Verification Methods of Seismic Performance

Table 20.17 shows the applicable verification methods of seismic performance. In the seismic design of highway bridges, it is important to increase the strength and the ductility capacity to appropriately resist the intensive earthquakes. The verification methods are based on static and dynamic analyses. In the JRA specifications, the static lateral force coefficient method with elastic design, ductility design method, and dynamic analysis are specified and these design methods shall be selected based on the configurations of bridge structures.

21212 Estimation of Demand

Once a performance objective has been defined, the next task is to determine if the design of the structure meets the stated performance objective. This means that a mathematical model of the structure is subjected to the seismic design loads (as specified by the hazard at the site in the previous step) and the demands on the system and its components are evaluated. The task of estimating seismic demand involves the determination of deformations and forces in both structural and nonstructural elements in the structure. model of the system is developed, the next step is to carry out an analysis of the model. This brings us to a crucial phase in the process. What kind of analysis is appropriate to accurately estimate the imposed seismic demands Since the motivation for moving away from traditional seismic design is to abandon linear force based methods, it can be argued that the analysis has to be nonlinear. In this context, pushover methods or nonlinear static approaches have gained...

2443 Earthquake Resistance

The simplest way to estimate the earthquake effect is a quasi-static model, in which the dynamic action of the ground motion is simulated by a static action of equivalent loads. The manner in which the equivalent static loads are established is introduced in many seismic design codes of different countries. In the region where the maximum vertical acceleration is 0.05g, usually the earthquake effect is not the governing factor in design and it is not necessary to check the forces induced by vertical or horizontal In the case of more complex structures or large span, dynamic analysis such as response spectrum method for modal analysis should be used. Such a method gives a good estimate of the maximum response during which the structure behaves elastically. For space frames, the vertical seismic action should be considered. However, few recorded data on the behavior of such a structure under vertical earthquake exist. In some seismic design codes, the magnitude of the vertical component...

21213 Assessment of Performance

The introduction of acceptance criteria for different performance levels represents a significant departure from traditional seismic design and is obviously the singular step in the overall process that qualifies the term ''performance based'' in the terminology of structural design. To develop acceptance criteria for a range of element types, it is necessary to have access to information on physically observed damage states during laboratory testing of components and subassemblies. FEMA-356 and ATC-40 provide an initial compilation of such data based on the input of experts and must be regarded as a preliminary guideline for use in the evaluation of existing structures. What is important is that the framework now exists to establish new acceptance limits and engineers have the flexibility to develop their own data using the results of experimental research.

102 Wood as a Material

Finally, ductility and energy dissipation, which are important concepts for seismic design, are beneficial for most wood structures. Provided the structure's connections are detailed properly, timber structures have relatively high values of ductility and energy dissipation. Provided the connections yield, such as would occur for nail and small-diameter bolted connections, ductilities in the range of 4 to 8 are not uncommon. Energy dissipation, on the other hand, from a material standpoint is very low for wood.

852 Isolation from seismic motion

The principle of isolation is simply to provide a discontinuity between two bodies in contact so that the motion of either body, in the direction of the discontinuity, cannot be fully transmitted. The discontinuity consists of a layer between the bodies which has low resistance to shear compared with the bodies themselves. Such discontinuities may be used for isolation from horizontal seismic motions of whole structures, parts of structures, or items of equipment mounted on structures. Because they are generally located at or near the base of the item concerned, such systems are often referred to as base isolation (Figure 8.11), although the generic term seismic isolation is preferable. Figure 8.11 Different locations for base isolation of buildings (from Mayes et al., 1984) (Reproduced by permission of the Earthquake Engineering Research Institute) The layer providing the discontinuity may take various forms, ranging from very thin sliding surfaces (e.g. PTFE bearings), through...

20623Displacement Demands on Bridges and Ductile Components

Seismic demands on bridge systems and ductile components are measured in terms of displacements rather than forces. Displacement demands shall be estimated from either equivalent static analysis (ESA) or elastic dynamic analysis (EDA, i.e., elastic response spectrum analysis) for typical bridge periods of 0.7 to 3 s. Attempts should be made to design bridges with dynamic characteristics (mass and stiffness) so that the fundamental period falls within the region between 0.7 and 3 s where the equal displacement principle applies. For short period bridges, linear elastic analysis typically underestimates displacement demands. In these cases, the inability to accurately predict displacements can be overcome by either designing the bridge to perform elastically, multiplying the elastic displacement from analysis by an amplification factor, or using seismic isolation and energy dissipation devices to limit seismic response. For long period (T> 3 s) bridges, a linear elastic analysis...

3132 Hazard Identification

A hazard identification is performed by selected professionals and the purpose of hazard identification is to identify all conceivable and relevant hazards. Typically a team of 6 to 10 experts, including naval architects, structural engineers, machinery engineers, surveyors, human factor engineer, marine officers and meeting moderator, provide the necessary expertise for the topic under study. The hazards are identified using historical incident databases and expertise of the team. Several analysis methods are available, including FMEA, HAZOP etc. The identified scenarios are ranked by their risk levels, and prioritizing hazards are given a focus and may be subjected to more detailed analysis.

2412 Definition of Space Frame

If one looks at technical literature on structural engineering, one finds that the meaning of the space frame has been very diverse or even confusing. In a very broad sense, space frame is literally a three-dimensional structure. However, in a more restricted sense, space frame means some type of special structural action in three dimensions. Sometimes, structural engineers and architects fail to convey what they really mean by the term. Thus it is appropriate to define here the term space frame as understood throughout this section. It is best to quote a definition given by a Working Group on Spatial Steel Structures of the International Association on Shell and Spatial Structures 1

Observations On Existing Models

The differential equation methods used in modeling and the optimization approaches used in geostatistics are closely related. The similarities are explored in variational calculus, a well-known mathematical specialty that relates differential equations to global minimization problems (Garabedian, 1964 Hildebrand, 1965 Stakgold, 1968). Such approaches are not new for instance, structural engineers have employed differential equation models side by side with equivalent minimum total strain energy methods for decades. In the fluid dynamics context, the solution to the Laplace equation 92p 3x2 + 92p 9y2 + 92p 3z2 0, subject to appropriate boundary conditions, can be exactly translated into a variational problem that minimizes an energy-like integral, in particular,

74 Business Interruption

Table 7.5 Deaths by structural and other causes in the 1994 Northridge, California earthquake (Reprinted from Durkin, ME (1996) Casualties patterns in the 1994 Northridge, California earthquake. 11th World Conference a Earthquake Engineering, Paper No. 979, with permission from Elsevier science)

2121 Elements of a Typical Performance Based Methodology

Rehabilitation of existing buildings. A parallel effort that resulted in the publication of ATC-40 (1996) is limited to RC buildings but is more comprehensive in its treatment. At least one other guideline that builds on FEMA-273 is the result of the FEMA-sponsored SAC project that produced FEMA-350 (2000). Other notable research that addresses issues in performance-based engineering includes ongoing efforts at the Mid-America Earthquake (MAE) and Pacific Earthquake Engineering Research (PEER) centers.

972 Limitations on Concentric Braced Frames

Figure 9.12 shows some of the common bracing configurations for concentric braced frames. Seismic design requirements vary with bracing configuration. Selection of R. Once concentric bracing is selected for seismic design, the force reduction factor, R, must be chosen. The discussion to this point has focused on ordinary braced frames, which have R 5.6, and also have the fewest restrictions on their application. This R value is somewhat smaller than that permitted for special steel moment-resisting frames, because concentrically braced frames are known to be dominated by brace buckling. As a result, their resistance may deteriorate and the brace may fracture under seismic loading. There are two major options for improving the behavior of concentrically braced frames. First, they may be used as a dual system with a special steel moment-resisting frame, and R 6.5. With this system, the moment frame must be able to resist the loads which are at least 25 of the total seismic design base...

533 Moment Connections

Stiffened Seat Connection

The most commonly used moment connection is the field welded connection shown in Fig. 5.56. This connection has been in common use throughout the U.S. for many years. In current seismic design covered by the AISC ''Seismic Provisions for Structural Steel Buildings,'' it is permitted for use in ordinary moment-resisting frames (Art. 9.7) without requirements for physical testing. It is also permitted for use in special moment-resisting frames, when the member sizes used for the specific project have been tested to demonstrate that the required ductility level can be achieved. Furthermore, it is widely used in areas of low seismicity where the AISC seismic provisions do not apply, and in frames designed primarily for wind and gravity forces, such as in the following example.

35314 Viscous Fluid Dampers

In several other applications, VF dampers were used in combination with seismic isolation systems. For example, VF dampers were incorporated into base isolation systems for five buildings of the new San Bernardino County Medical Center, located close to two major fault lines, in 1995. The five buildings required a total of 233 dampers, each having an output force of 320,000 lbs and generating an energy dissipation level of 3,000 horsepower at a speed of 60 in. s. A layout of the damper-isolation system assembly is shown in Figure 35.18 and Figure 35.19 gives the dimensions ofthe viscous dampers employed.

1957 Analysis Procedures

The shape of the design response spectrum shown in Figure 19.11 is not representative of the dynamic characteristics of ground motion found close to the fault rupture zone. Such motions are often dominated by a large velocity pulse and very large spectral displacement demands. Therefore, for structures in SDCs E and F, the seismic design categories for structures located close to major active faults, the base

1956 Design Coefficients

Under the NEHRP Provisions, required seismic design forces and, therefore, required lateral strength is typically determined by elastic methods of analysis, based on the elastic dynamic response of structures to design ground shaking. However, since most structures are anticipated to exhibit inelastic behavior when responding to the design ground motions, it is recognized that linear response analysis does not provide an accurate portrayal of the actual earthquake demands. Therefore, when linear analysis methods are employed, a series of design coefficients are used to adjust the computed elastic response values to suitable design values that consider probable inelastic response modification. Specifically, these coefficients are the response modification factor, R, the overstrength factor, fi0, and the deflection amplification coefficient, Cd. Tabulated values of these factors are assigned to a structure based on the selected structural system and the level of detailing employed in...

35313 Viscoelastic Dampers

Seismic applications of VE dampers to structures began more recently. A seismic retrofit project using VE dampers began in 1993 for the 13-story Santa Clara County building in San Jose, CA (Crosby et al. 1994). Situated in a high seismic risk region, the building was built in 1976. It is approximately 64 m in height and nearly square in plan, with 51 x 51 m on typical upper floors. The exterior cladding consists of full-height glazing on two sides and metal siding on the other two sides. The exterior cladding, however, provides little resistance to structural drift. The equivalent viscous damping in the fundamental mode is less than 1 of critical.

1522 Seismic Analysis Of Cablesuspended Structures

(Guide Specifications for Seismic Design of Highway Bridges,'' American Association of State Highway and Transportation Officials Guidelines for the Design of Cable-Stayed Bridges,'' ASCE Committee on Cable-Stayed Bridges. A. M. Abdel-Ghaffar, and L. I. Rubin, ''Vertical Seismic Behavior of Suspension Bridges,'' The International Journal of Earthquake Engineering and Structural Dynamics, vol. 11, January-February, 1983.

Pressure Vesels In Civil Engineering

Legs, erection of vessels with, 394 Legs, seismic design for braced calculations, 135-136 dimensional data, 133 flow chart for, 138 legs and cross-bracing, sizes for, 137 load diagrams, 134 loads, summary of, 136 notation, 132 Legs, seismic design for unbraced calculations, 127-129 Legs, seismic design for unbraced (Continued) dimensional data, 126 leg configurations, 126 leg sizing chart, 131 notation, 125 vertical load, 130 Leg supports, 109-110 full circular base plate design, 424 loads, 435-436 nozzle flange check, 423 sample problem for top, 427 130 side, 422, 435, 436 tension, maximum, 423 top, 422, 435 136 Lugs, seismic design for

Design Of Vessel Supports 109

Procedure 3-3 Seismic Design for Vessels, 120 Procedure 3-4 Seismic Design Vessel on Unbraced Legs, 125 Procedure 3-5 Seismic Design Vessel on Braced Legs, 132 Procedure 3-6 Seismic Design Vessel on Rings, 140 Procedure 3-7 Seismic Design Vessel on Lugs 1, 145 Procedure 3-8 Seismic Design Vessel on Lugs 2, 151 Procedure 3-9 Seismic Design Vessel on Skirt, 157

973 Eccentric Braced Frames

These combine the strength and stiffness of a concentric braced frame with the inelastic performance of a special moment-resisting frame (Fig. 9.9c). The UBC permits use of an R of 7 or 8.5 for an eccentric braced frame. This results in seismic design forces comparable to those required for special moment-resisting frames if the fundamental period of vibration is the same. However, braced frames are invariably stiffer than moment-resisting frames of similar geometry and have a shorter period. This results in a somewhat larger design load than for special moment-resisting frames under comparable conditions. (C. W. Roeder, and E. P. Popov, Eccentrically Braced Steel Frames for Earthquakes,'' Journal of Structural Division, March 1978, American Society of Civil Engineers.) Eccentrically Braced Frames in Dual Systems. The preceding discussion has covered eccentrically braced frames with R 7.0. Eccentrically braced frames may also be designed as part of dual systems with special...

15191 Static Analysis Elastic Theory

Static System Cable Stayed Bridge

The secondary effect of creep of cables (Art. 15.12) can be incorporated into the analysis. The analogy of a beam on elastic supports is changed thereby to that of a beam on linear viscoelastic supports. Better stiffness against creep for cable-stayed bridges than for comparable suspension bridges has been reported. (K. Moser, Time-Dependent Response of the Suspension and Cable-Stayed Bridges,'' International Association of Bridge and Structural Engineers, 8th Congress Final Report, 1968, pp. 119-129.)

123 Introduction of the Reliability Based Structural Design Concept

The analytical procedures used to estimate the load effects are identical in ASD and LRFD approaches. Thus, the analytical procedures, computer programs, and other analysis aids used for ASD are also applicable for LRFD. Only the treatments of load effects are different in the two concepts. The nominal resistance is also calculated deterministically using a codified approach. The capacity reduction factor is used to address the level of uncertainty in estimating it. As pointed out earlier, for wider applications, LRFD or reliability-based design guidelines were calibrated with respect to time-tested ASD procedure. Thus, in many cases, the final selection of a structural member will be identical for ASD and the reliability-based design concept however, the design procedures will be very different as outlined below. Using the reliability-based design concept, structural engineers will be more empowered to manage risk in a typical design.

183 Damage as a Result of Structural Problems 1831 Foundation Failure

FIGURE 18.21 Damage to the Lower San Fernando Dam. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.21 Damage to the Lower San Fernando Dam. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.22 Closer view of damage to the Lower San Fernando Dam. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.22 Closer view of damage to the Lower San Fernando Dam. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.23 Aerial view of Lower San Fernando Dam and San Fernando Valley. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.)

2092 Performance Based Design Specifications

The code structure of the JRA Seismic Design Specifications is as shown in Figure 20.31. The static and dynamic verification methods of the seismic performance as well as the evaluation methods of the FIGURE 20.31 Code structure of JRA seismic design specification. FIGURE 20.31 Code structure of JRA seismic design specification.

194 Types of Buildings and Typical Earthquake Performance

There are many different types of buildings, with varying kinds of earthquake performance and seismic design needs. This section discusses general earthquake performance of buildings, with the emphasis more toward those buildings typically built in the western United States. Specific aspects of structural analysis and design of buildings, other structures, steel, concrete, wood, masonry, and other topics are discussed in other chapters. The typical earthquake performances of different types of common building structural systems are described in this section to provide insights into seismic design for buildings.

99 Member And Connection Design For Lateral Loads

Seismic design loads are determined by the static-force or dynamic methods. With the static-force method, the total base shear is determined by Eq. (9.5). It is distributed to bents and structural elements by simple rules combined with considerations of the distribution of mass and stiffness (Art. 9.4). With the dynamic method, the total range of dynamic modes Connections used in seismic design are normally unrestrained or FR connections. PR connections have less seismic resistance than the members they are connecting, and therefore inelastic deformations during severe earthquakes are concentrated in the connections. PR connections have limited energy-dissipation capacity. Furthermore, the total ductility and deformation capacity of a structural frame under cyclic loading is uncertain, and the energy dissipation is concentrated in the connections. These combined effects have limited the use of PR connections in seismic design. Nevertheless, they offer many advantages and may be...

95 Dynamic Method Of Seismic Load Distribution

The Uniform Building Code'' static-force method (Art. 9.4) is based on a single-mode response with approximate load distributions and corrections for higher-mode response. These simplifications are appropriate for simple. regular structures. However, they do not consider the full range of seismic behavior in complex structures. The dynamic method of seismic analysis is required for many structures with unusual or irregular geometry, since it results in distributions of seismic design forces that are consistent with the distribution of mass and stiffness of the frames, rather than arbitrary and empirical rules. Irregular structures include frames with any of the following characteristics

182 Damage as a Result of Problem Soils 1821 Liquefaction

FIGURE 18.4 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.4 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.5 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.5 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.)

10 987654321

For ease of reading, the chapters are divided into six sections. Section I presents fundamental principles of structural analysis for static and dynamic loads. Section II addresses deterministic and probabilistic design theories and describes their applications for the design of structures using different construction materials. Section III discusses high-performance materials and their applications for structural design and rehabilitation. Section IV introduces the principles and practice of seismic and performance-based design of buildings and bridges. Section V is a collection of chapters that address the behavior, analysis, and design of various special structures such as multistory rigid and semirigid frames, short- and long-span bridges, cooling towers, as well as tunnel and glass structures. Section VI is a miscellany of topics of interest to structural engineers. In this section are included materials related to connections, effective length factors, bracing, floor system,...

Further Reading

Chen and Scawthorn (2002) provide an extensive reference on earthquake engineering, while Naiem (2001) provides an excellent resource on seismic design. Both references have individual chapters on design of steel, wood, reinforced concrete, reinforced masonry, and precast structures, and also on nonstructural elements. SEAOC (1999), BSSC (1997), and SEAOC (1996) provide an excellent overview of the current state of seismic design requirements. U.S. Army (1992) and Dowrick (1987) are also useful, although a bit older. Some useful sources on seismic code provisions in countries other than the U.S. include Earthquake Resistant Design Codes in Japan (2000), Paz (1995), and IAEE (1996). The last is a comprehensive compendium of seismic regulations for over 40 countries, including Eurocode 8 (the European Union's seismic provisions).

201 Introduction

Bridges are very important elements in the modern transportation system. Recent earthquakes, particularly the 1989 Loma Prieta and the 1994 Northridge Earthquakes in California, the 1995 Hyogo-Ken Nanbu Earthquake in Japan, the 1999 JiJi Earthquake in Taiwan, and the 1999 Kocaeli Earthquake in Turkey, have caused collapse of, or severe damage to, a considerable number of major bridges 1,2 . Since the 1989 Loma Prieta Earthquake in California 3 , extensive research 4-18 has been conducted on seismic design and retrofit of bridges in Japan and the United States, especially in California. *Much of the material of this chapter was taken from Duan, L. and Chen, W.F., Chapter 19 Bridges, in Earthquake Engineering Handbook, Chen, W.F. and Scawthorn, C., Ed., CRC Press, Boca Raton, FL, 2002. This chapter first addresses the seismic bridge design philosophies and conceptual design in general, then discusses mainly the U.S. seismic design practice to illustrate the process, and finally presents...

851 Introduction

According to Robinson (1998) Very strong support for the principles of seismic isolation is given by the results of the January 1994 Los Angeles earthquake. The fact that of the 10 hospitals affected by the Los Angeles earthquake, only the hospital seismically isolated by a lead-rubber bearing system was able to continue to operate. This seven-storey hospital (the University of Southern California Teaching Hospital) underwent ground accelerations of 0.49 g, while the rooftop acceleration was 0.21 g, that is an attenuation by a factor of 1.8. The Olive View Hospital, nearer to the epicentre of the earthquake, underwent a top floor acceleration of 2.31 g compared with its base acceleration of 0.82 g, a magnification by a factor of 2.8. It is interesting to note that the Kobe (Hyogo-ken Nanbu) earthquake of January 17, 1995 led to a sudden and significant change in application of passive control technologies for seismic design in Japan. In the three-year period prior to the 1995...

142 071

Figure 10.46 Load-deflection behaviour of concrete masonry test walls with high aspect ratio (Reprinted from Paulay, T. and Priestley, MJN (1992), Seismic Design of Reinforced Concrete and Masonry Buildings. Copyright (1992). Reprinted by permission of John Wiley & Sons, Inc.)

Bridges

20.3 Seismic Design 20-3 20.6 Seismic Design 20-13 ATC MCEER Guidelines Caltrans Seismic Design Criteria 20.9 Seismic Design Practice in Japan 20-46 Introduction Performance-Based Design Specifications Basic Principles of Seismic Design Ground Motion and Seismic Performance Level Verification Methods of Seismic Performance

67 Seismic Loads

The engineering approach to seismic design differs from that for other load types. For live, wind, or snow loads, the intent of a structural design is to preclude structural damage. However, to achieve an economical seismic design, codes and standards permit local yielding of a structure during a major earthquake. Local yielding absorbs energy but results in permanent deformations of structures. Thus seismic design incorporates not only application of anticipated seismic forces but also use of structural details that ensure adequate ductility to absorb the seismic forces without compromising the stability of structures. Provisions for this are included in the AISC specifications for structural steel for buildings.

96 Future Challenges

9.6.1 Performance-Based Seismic Design of Masonry Structures Across the entire spectrum of construction materials, increased attention has been focused on performance-based seismic design, which can be defined as design whose objective is a structure that can satisfy different performance objectives under increasing levels of probable seismic excitation. For example, a structure might be designed to remain operational under a design earthquake with a relatively short recurrence interval, to be capable of immediate occupancy under a design earthquake with a longer recurrence interval, to ensure life safety under a design earthquake with a still longer recurrence interval, and to not collapse under a design earthquake with a long recurrence interval. This design approach, accepted qualitatively since the 1970s, has been adopted quantitatively in recent documents related to seismic rehabilitation (FEMA 356 2000), and will probably be incorporated into future seismic design provisions for...

107 Shear Walls

The perforated shear wall method is included in the NEHRP Provisions (Building Seismic Safety Council 2003a,b) and the 2003 IBC (International Code Council 2000a) for use in seismic design. It had been adopted earlier for wind design by the Building Officials and Code Administrators (BOCA) and Southern Building Code Congress International (SBCCI) building codes. The method is an empirical design method that accounts for the added resistance provided by the wall segments above and below window and door openings in the wall, if they are sheathed with equivalent sheathing to that used in the fully sheathed segments of the wall. The method was originally developed by Sugiyama and Matsumoto (1994) using reduced-scale light-frame wall specimens, and the method was

Aircraft

Developments of aircraft turbine intake engine blades that started during the early 1940s may now reach fulfillment. Major problem in the past has been to control the expansion of the blades that become heated during engine operation. The next generation of turbine fan blades should significantly improve safety and reliability, reduce noise, and lower maintenance and fuel costs for commercial and military planes because engineers will probably craft them from carbon fiber RP composites. Initial feasibility tests by University of California at San Diego (UCSD) structural engineers, NASA, and the U.S. Air Force show these carbon composite fan blades are superior to the metallic, titanium blades currently used.

Stiffeners

For statically loaded structures, which include structures subjected to wind and seismic loads, this flexing is not detrimental to structural safety and may even be desirable in seismic design because it allows more energy absorption in the members of the structure and it reduces premature fracture in the connections. For buildings, the AISC seismic specification has detailing requirements to allow gussets to flex in certain situations. AISC ASD and LRFD manuals include requirements regarding gusset stability. It is important that gusset buckling be controlled to prevent changes in structure geometry that could render the structure unserviceable or cause catastrophic collapse (see also Art. 5.36).

Structures

21.1 Some Issues in Current Seismic Design 21-2 Performance-based design (PBD) has emerged as the new paradigm in seismic engineering. The concept of PBD is not limited to the field of seismic design, though the material covered in this chapter focuses primarily on recent developments in earthquake engineering. Performance-based seismic engineering (PBSE) is still an evolving methodology hence, the information presented in this chapter should not be interpreted as an existing design specification or an adopted standard. Rather, the contents of this chapter should be viewed as an introduction to an emerging concept for seismic design of building systems. There are several completed and ongoing efforts to develop performance-based seismic design methodologies. Published documents such as ATC-40 (1996), FEMA-350 (2000), and FEMA-356 (2000) embody key aspects of PBD however, they were each developed with limited objectives. FEMA-350 applies to new steel moment frames only. ATC-40 and...

1823 Weak Clay

Structural Engineering Handbook

FIGURE 18.17 Aerial view of Turnagain Slide. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.17 Aerial view of Turnagain Slide. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.18 About 75 homes were damaged as a result of the Turnagain Heights Slide. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.18 About 75 homes were damaged as a result of the Turnagain Heights Slide. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.20 Landslides at Pacoima Dam following the 1971 San Fernando Earthquake. (Photograph courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.20 Landslides at...

0024489

In the context of education of future structural engineers, the presence of uncertainty must be identified in design courses. Reliability assessment methods can contribute to the transition from deterministic to a probabilistic way of thinking for students as well as designers. In the United States, the Accreditation Board of Engineering and Technology now requires that all civil engineering undergraduate students demonstrate knowledge of the application of probability and statistics to engineering problems, indicating its importance in civil engineering education. Under the sponsorship of the Pacific Earthquake Engineering Research (PEER) Center 31 , a multiuniversity team developed a general-purpose finite element reliability code within the framework of OpenSees. A web address is given in the references for further information on the program 31 . Structural engineers without a formal education in reliability-based design may not be able to use these computer programs. They can be...

Conversion Factors

This section gives general requirements for structural detailing in concrete. A slight departure from these requirements can be expected because each project is different. Individual structural engineers and designer detailers also influence the style of working drawings and schedules. Moreover, structural detailing in concrete can vary since it can be considerably affected by external requirements including those of authorities such as gas, electricity, water, municipal, etc. Full drawings are prepared by structural engineers acting as consultants as part of the tender documentation. The architects are involved in the preparation of the site and other general arrangement plans. The main contractors are involved in preparation of temporary work drawings, including shoring and formwork. During the contract, drawings are sometimes modified by minor amendments and additional details. These drawings are generally updated as the projects progress. The drawings, which are distributed to...

Vfy Cladding

Official recommendations for seismic design of prestressed concrete Some organizations interested in the use of prestressed concrete have published seismic design recommendations. For example, the FIP (1977) in addition to the New Zealand concrete code (NZS 3101, 1995), gives guidance on this subject. In contrast, the major

1835 Shear

Kobe Earthquake

FIGURE 18.48 West elevation of the Mt. McKinley Apartment building after the 1964 Great Alaska Earthquake. (Photograph by Karl Steinbrugge, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.48 West elevation of the Mt. McKinley Apartment building after the 1964 Great Alaska Earthquake. (Photograph by Karl Steinbrugge, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.49 Damage to north side of Mt. McKinley Apartments. (Photograph by Karl Steinbrugge, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.49 Damage to north side of Mt. McKinley Apartments. (Photograph by Karl Steinbrugge, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.50 Damage to the south side of Mt. McKinley Apartments. (Photograph by Karl Steinbrugge, Earthquake Engineering Research Center, University of California, Berkeley.) FIGURE 18.50 Damage to the south side of Mt....

321Introduction

This chapter presents an overview of aspects related to the design of structural bracing used in beams, columns, and frame structures and is intended for practicing civil and structural engineers. Many of the design guidelines presented were incorporated into the 2002 Load and Resistance Factor Design Manual published by the American Institute of Steel Construction (AISC). The intended focus is on simplicity and ease of implementation over exact formulations. The basis for the design formulations along with a classification system for bracing systems is first presented. Design formulations are presented with illustrative numerical examples. Finally, common faulty bracing details are presented.

191Introduction

Seismic design involves two distinct steps determining (or estimating) the forces that will act on a structure and designing the structure so as to both resist these forces and keep deflections within prescribed limits. This chapter provides a basic explanation of the seismic design of buildings, by first discussing how earthquake forces are caused in buildings and the systems that have been developed to deal with these forces, then reviewing the most common types of buildings and their typical seismic performance, then discussing selected key aspects of seismic design, and, finally, discussing the force-determination aspect currently used in building codes.

341 Introduction

This section of the handbook presents an overview of information useful to structural engineers in evaluating the fatigue and fracture limit states of steel, aluminum, and concrete structural components. Topics include materials selection, design, and detailing for new structures, as well as assessment of existing structures. The emphasis of this chapter is on structural steel components, since aluminum and other metal components are not common in the primary load-carrying systems of most civil structures. Fatigue of concrete components is covered only briefly since it is rarely a significant problem. As a practical matter, fracture of concrete is checked by usual strength design calculations and therefore is not covered here. The fracture mechanics of concrete is covered elsewhere 1 .