20827Concrete Design Requirements

20.8.2.7.1 Limiting Longitudinal Reinforcement Ratios

The ratio of longitudinal reinforcement to the gross cross-section shall not be less than 0.01 and 0.005 for columns and pier walls, respectively, and not more than 0.04.

20.8.2.7.2 Transverse Reinforcement in Plastic Hinge Zones

For confinement in plastic hinge zones (larger of 1.5 times cross-sectional dimension in the direction of bending and the regions of column where the moment exceeds 75% of overstrength plastic moment, transverse reinforcement shall not be less than [27]

f-'/Ag \/ 1.25Pe\ „ 0.45^M - 11(0.5 + —-e for D < 0.9m r =1 fy c fc Ag 7 (20 59)

For ties

03si(J - 1)(0.5 + f^) Ash,min = larger of ^ f c 1 25p lc g (20 . 60)

TABLE 20.13 Caltrans Limiting Width-Thickness Ratios [36]

Description of elements

Width-thickness Examples ratios

Unstiffened elements

1 Flanges of I-shaped rolled beams and channels in flexure

2 Outstanding legs of pairs of angles in continuous contact; flanges of channels in axial compression; angles and plates projecting from beams or compression members

Stiffened elements

3 Flanges of square and rectangular boxes and hollow structural section of uniform thickness subject to bending or compression; flange cover plates and diaphragm plates between lines of fasteners or welds

4 Unsupported width of cover plates perforated with a succession of access holes

5 All other uniformly compressed stiffened elements, i.e., supported along two edges

6 Webs in flexural compression

7 Webs in combined flexural and axial compression

Figure 20.27a Figure 20.27c

Figure 20.27d Figure 22.27e

Figure 20.27b

Figure 20.27d

8 Longitudinally stiffened plates in compression

9 Round HSS in axial compression or flexure

Figure 20.27e b/t b/t b/t b/t b/t h/tw h/tw h/tw b/t D/t

0 0

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