In view of present accepted practice in this country in this technological area, common U.S. units measurement have been used throughout this paper. In recognition of the position of the USA as a signaton to the General Conference on Weights and Measures, which gave official status to the metric SI systems units in 1960, we assist readers interested in making use of the coherent system of SI units, by giving co version factors applicable to U.S. units used in this paper. Compressive Strength of Slender Concrete Masonry Walls* Felix Y. Yokel, Robert G. Mathey, and Robert D. Dikkers Sixty reinforced and unreinforced concrete masonry walls of different slenderness ratios were tested to failure under vertical loads applied axially and at various eccentricities. Prism specimens, made of similar masonry units and mortars, were also tested under the same loading conditions. Analysis of test results indicates that wall strength can be conservatively predicted by evaluating cross-sectional wall capacity on the basis of prism strength and reducing the capacity for slenderness effects by evaluating the added moments attributable to wall deflection. Test results were also compared with allowable loads computed in accordance with the current NCMA standard. Key words: Buckling; compressive strength; concrete block walls; elastic stability; flexural strength; masonry walls; reinforced concrete masonry walls; slenderness effect; structural stability. 1. Introduction and Objective At the present time only a limited amount of exerimental data is available on the compressive rength of slender concrete masonry walls. Present esign practice accounts for slenderness effects by ress correction factors [1]1 or empirical equations 2]. The designer has no rational method by which e can evaluate slenderness effects, and important arameters such as cross-sectional properties, end upport conditions, and the relationship between ompressive strength and elastic properties of the asonry are not taken into consideration. The objectives of this investigation were to deterine and analyze the effects of wall slenderness and ad eccentricity on the strength of slender concrete asonry walls. This analysis was intended to epresent a step in the development of rational esign methods for masonry walls subjected to axial nd eccentric vertical loads. 2. Scope Two wall systems representing reinforced and uneinforced masonry construction were tested: 1. 6-in reinforced concrete masonry walls. *This work was performed with the aid of a financial grant from he National Concrete Masonry Association (NCMA). 1 Figures in brackets indicate literature references listed in sec For each of these wall systems specimens were constructed which were 4-ft wide and approximately 10, 16, and 20-ft high.2 These walls were tested to destruction under vertical loads which were applied axially and at eccentricities of, and of the wall thickness. For each combination of wall height and load eccentricity, two companion specimens were tested. One of these specimens was instrumented to measure horizontal deflections and wall shortening under vertical loads. All of these specimens were tested at an approximate age of ten days. In addition, two 10-ft high and two 20-ft high walls of each wall system were tested axially at an age of more than 28 days to determine the strength increase with an additional curing period. Following construction, four of the unreinforced walls were found to have undersized block and increased joint thicknesses as a consequence. These specimens were tested, and an additional four specimens with correct joint size were added to provide unbiased data. As indicated in table 2.1, a total of 28 reinforced walls and 32 unreinforced walls were tested. An investigation of masonry prism strength under eccentric compressive loads was also conducted by subjecting 8-in and 6-in masonry prisms to the same loading conditions that were used for the full scale 2 Hereafter in this report heights of walls are referred to as 10 ft, 16 ft and 20 ft. However, actual wall heights were 9 ft-3 in, 15 ft11 in and 19 ft-3 in. on 10. sive strength of the units tested was 4230 psi and 4080 psi for the 8-in and the 6-in units, respectively. The masonry units used are illustrated in figure 3.1. Dimensions and properties of the masonry units which were determined in accordance with ASTM standard C140-65T [3] are recorded in table 3.1. 3.1.2. Mortar The units were made of a blend of light and normal weight aggregate (cinder and limestone) and were autoclaved. Cementitious material was portland cement and silica flour. The specified compressive strength of the units, based on net cross-sec- The mortar used in all wall panels was type S mortional area, was 3,000 psi. Actual average compres- tar, in accordance with the proportion specifications Dimensions and Properties of Concrete Masonry Units/ TABLE 3.1 a/ Values given in the table represent the average results from tests or measurements of 5 units. Forty-one sets of 2-in mortar cubes were made ring the fabrication of the wall panels. The mortar bes were made and stored under the same condions as the wall panels. In general, the mortar cubes ere tested at approximately the same age as the rresponding walls. However, some of the reinrced concrete masonry wall panels took 6 days to bricate because of waiting time for two grouting perations and weekend delays. The age of tested ortar cubes, therefore, ranged from 7 to 53 days. lortar cube strength averaged 1180 psi. Individual ortar cube tests are listed in table 3.2. As indicated the table, the cube strengths ranged from 700 to 768 psi. However, 30 of the 41 sets of cubes had ›mpressive strengths within 300 psi of the average alue. TABLE 3.2 Since many batches of mortar were used in the construction of a wall panel and many of the walls took up to 6 days to fabricate, the mortar strength varied in different elevations of the wall. The average mortar strength was 1180 psi. 3.1.3. Grout Compressive Strength of Mortar Cubes |