Masonry Magazine July 1976 Page. 13
NCMA-TEK
An Information series from National Concrete Masonry Association
Concrete Masonry Wall Beams
Introduction
Wall panels, which span as beams between end supports instead of functioning as bearing walls with continuous line support along the bottom, are often referred to as "wall beams." Since such walls do act as beams, they may be designed according to provisions applicable to flexural members and do not have to comply with h/t limitations of bearing walls (maximum of 30 for reinforced concrete masonry walls). Accordingly, for various building applications, such as commercial, industrial or other buildings, where there is need for large wall panels, concrete masonry wall beams may provide an effective and economical design solution.
Research
Tests have been conducted on concrete masonry wall beams by the Masonry Institute of America, in cooperation with the Concrete Masonry Association of California and the Construction Division of The Boise-Cascade Corporation. The results of such tests have been briefly described in a three-part article published by the Masonry Industry magazine (1). The dimensions and various construction features of the wall beams tested are shown in Figure 1. Reinforcement in the wall panels tested was basically the minimum steel area required (0.002 times the wall cross-sectional area) and was spaced 4 ft. o.c. In panel A, some additional short bars were provided as vertical stirrups near each end. In panel B, there was some additional steel provided at the top center under the applied load; some bars provided in vertical cells adjacent to the bottom supports; and a slightly larger horizontal bar provided in the bottom course.
Panel A cracked under the upper bearing plate at an initial load of 80 kips, then carried 120 kips on reloading. No distress was observed in the overall panel, merely the local failure at the top. Panel B initially failed under the upper bearing plate at a load of 100 kips, with some spalling under the plate at 40 kips. After the initial test, a concrete beam was poured on top of the wall beam to distribute the load and the wall beam was then loaded to 246 kips. Failure occured at one of the supports and was due to improper grouting in the wall panel.
Based on the tests conducted, the International Conference of Building Officials (ICBO) has issued a Research Recommendation covering the design of concrete masonry deep wall beams (2). Excerpts from this research recommendation are given in the following paragraphs.
"Description: General: The deep beam wall system consists of concrete masonry panels constructed in running bond only and in accordance with Chapter 24 of the Uniform Building Code, except for h/t limitations for load-bearing elements and a different load reduction equation for allowable axial stresses due to the deep beam considerations. Reinforcement complies with Section 2418 (1) 3 with additional reinforcement, as required
FIGURE 1. Description of Wall Beams Tested
Panel | h | l | b | h/b
------- | -------- | -------- | -------- | --------
A | 24' | 24' | 7.5" | 38
B | 18' | 24' | 5.5" | 39
PANEL MATERIALS: Mortar - Type S (ASTM C270)
Grout - Panel A-1:3:2 (Course grout)
Panel B-1:3 (Fine grout)
Block- ASTM C90
Reinforcement - Conventional grade (ASTM C615)
TEK 78 0 1976 National Concrete Masonry Association
"See list of references at the end of this TEK bulletin.