Details of Check for Boundary Element Requirements

Size: px

Start display at page:

Download "Details of Check for Boundary Element Requirements"

Meghan Jordan
5 years ago
Views:

1 COMUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001 SHEAR WALL DESIGN UCB 97 Technical te Wall ier Bondary Elements This Technical te describes how the program considers the bondary element reqirements for each leg of concrete wall piers sing the 1997 UBC. The program ses an approach based on the reqirements of Section in the 1997 UBC. te that the bondary element reqirements are considered separately for each design load case that incldes seismic load. te: The program considers only the reqirements of section of the 1997 UBC in determining bondary element reqirements. Section is not considered by the program. Details of Check for Bondary Element Reqirements The following information is available for the bondary element check: The design forces, V and M for the pier section. The length of the wall pier, L p, the gross area of the pier, A g, and the net area of the pier, A cv. The net area of the pier is the area bonded by the web thickness, t p, and the length of the pier. Refer to Figre 1 in Technical te Wall ier Design Sections Shear Wall for an illstration of the dimensions L p and t p. The area of steel in the pier, A s. This area of steel is either calclated by the program or it is provided by the ser. The material properties of the pier, f c and f y. The symmetry of the wall pier (i.e., is the left side of the pier the same as the right side of the pier). Only the geometry of the pier is considered, not the reinforcing, when determining if the pier is symmetrical. Figre 1 shows some examples of symmetrical and nsymmetrical wall piers. te Details of Check for Bondary Element Reqirements age 1 of 6

2 Wall ier Bondary Elements a. Symmetrical c. Unsymmetrical b. Symmetrical d. Unsymmetrical Figre 1 Example lan Views of Symmetrical and Unsymmetrical Wall iers that a pier defined in Section Designer is assmed to be nsymmetrical nless it is made p of a single rectanglar shape. Using this information, the program calclates the vale of O, which is the nominal axial load strength of the wall sing Eqation 1. O = 0.85f c (A g - A s ) + f y A s Eqn. 1 te: For simplified design only, if there is a flexral failre in any design load combination, the program sets A s in Eqation 1 to zero for all design load combinations considered for the pier. After the vale of O is known, the program calclates for qantities that are sed to determine the bondary zone reqirements. These qantities are: O M V L p gf c A 3A cv f c The flowchart in Figre 2 illstrates the process the program ses to determine if bondary elements are reqired. te that if exceeds 0.35 O, the bondary element reqirements are not checked. This is based on 1997 UBC Section Details of Check for Bondary Element Reqirements age 2 of 6

3 Wall ier Bondary Elements Figre 2 Flowchart of the Is compression? rocess the rogram Uses to Determine if Bondary Elements Are Reqired Is Abs 0.35? O Bondary element reqirements are not checked Is wall symmetrical? Is Abs 0.05? Agf c Is Abs 0.10? Agf c Bondary elements are reqired M Is Abs 1.0? V L p M Is Abs 3.0? VL p Bondary elements are reqired Is Abs ( V ) 3A f? cv c Bondary elements are not reqired Details of Check for Bondary Element Reqirements age 3 of 6

4 Wall ier Bondary Elements If bondary elements are reqired, the program calclates the minimm reqired length of the bondary zone at each end of the wall, L BZ, according to the reqirements of Section in the 1997 UBC. The UBC reqires that L BZ vary linearly from 0.25L p to 0.15L p for, varying from 0.35 O to 0.15 O, and that L BZ shall not be less than 0.15L p. Based on these reqirements, the program calclates L BZ sing either Eqation 2a or 2b, depending on whether is compression or tension. When is compression: L = Eqn. 2a BZ Abs Lp 0.15L p 2 O When is tension: L BZ = 0.15L p Eqn. 2b Figre 3 illstrates the bondary zone length L BZ. L BZ L BZ L p Figre 3: Illstration of Bondary Zone Length, L BZ age 4 of 6

5 Wall ier Bondary Elements Example Figre 4 shows an example wall pier. The pier is 12.5 feet long. It is reinforced with #5 bars at 12 inches on center on each face. Refer to the figre for properties and forces. te: Bondary element reqirements are considered by the program for two- and threedimensional wall piers The calclations follow: = 1,000 kips (given) L p = 12.5 feet = 150 inches (given) A g = 12.5 ft * 1 ft = 12.5 ft 2 = 1,800 in 2 A s = 13 bars * 2 faces * 0.31 in 2 = 8.06 in 2 f c = 4 ksi (given) f y = 60 ksi (given) The pier is symmetrical. (given) O = 0.85f c (A g - A s ) + f y A s O = 0.85 * 4 (1, ) + 60 * 8.06 = 6,576 kips O 1,000 = = < 0.35 OK 6,576 A gfc 1,000 = = > 0.1 NG 1,800 * 4 Therefore bondary elements are reqired. 1,000 L BZ = * 150 = 22.7 inches 2 * 6,576 Example age 5 of 6

6 Wall ier Bondary Elements 12-6" # 5@12 o.c., each face 1 f c = 4 ksi fy = 60 ksi = 1000 kips V = 350 kips M = 3500 kips Figre 4: Wall ier Example Calclations Displaying the pier bondary zone data provides either the reqired bondary zone length, or "NC" (short for t Checked) if bondary zone reqirements are not checked becase / o > 0.35, or "NN" (short for t Needed) if bondary zones are not reqired. Example age 6 of 6

Copyright Canadian Institute of Steel Construction

Copyright Canadian Institute of Steel Construction Copyright 017 by Canadian Institte of Steel Constrction All rights reserved. This book or any part thereof mst not be reprodced in any form withot the written permission of the pblisher. Third Edition