` Seismic Enhancement of Partially Grouted Reinforced Masonry: Shear Friction Analysis Kerianne Westphal, NEES REU, Manhattan College, [email protected] Benson Shing , PhD., Andreas Koutras , University of California, San Diego The specimen met only the minimum code requirements (Shing, et al. 2014). Plan and elevation views of the specimen (Figure 2, Figure 3) display where the steel reinforcement was located in the structure and, therefore, where the structure contained grout. Figure 2 – Plan view of specimen one. Figure 3 – Elevation view of specimen one. The specimen failed rigidly. Figure 4 displays the types of damages that occurred within the structure during the shake table tests. One of the failure mechanisms was the sliding that occurred between the base of the structure and the concrete foundation, which was resisted by shear friction. Figure 4 – Typical damages to the masonry structure during shake table tests. FORMULA DERIVATION RESULTS CONCLUSIONS ACKNOWLEDGMENTS INTRODUCTION Reinforced masonry buildings are used to construct: • Schools • Industrial buildings • Public facilities (libraries) • Hospitals Two types West Coast: Areas of Full Grouting: • All masonry blocks are filled with grout • Seismically resilient Partial Grouting: • Only masonry blocks containing steel reinforcement are filled with grout • Economically competitive • Not as seismically resilient Middle America/East Coast: Areas of • Low seismic risk • Moderate seismic risk • High seismic risk • Moderate seismic risk • High seismic risk 1) 2) Current Formula: where V = nominal shear-friction strength μ = friction coefficient (1.0 for intentionally roughened surfaces, 0.70 for all other A st = area of steel rebar f y = yield strength P u = normal force Only valid for walls with shear-span ratio (height to length ratio) less than 0.5 (Figure 5), so that the wall is short and long. These walls are not controlled by bending and, therefore, can be governed by the formula currently used in ACI 318. Figure 5 – Short, long masonry wall for which the current shear friction formula is acceptable Looking at a wall whose shear span ratio is greater than 0.5 and is controlled by bending (Figure 6), only the side of the wall in compression will be able to produce a shear- friction against the foundation. This region has a distance: a = c*0.80 where a is the approximate distance of an equivalent rectangular force. Therefore, the equivalent shear friction formula for this case and it’s subsequent simplifications are as follows: Force, P Compression Tension a = c*0.80 Figure 6 – Tall, small in height masonry wall for which the new shear friction formula applies. where μ = .65 a = 0.80*c t = wall thickness f’m = masonry strength A nc = net area in compression 0 20 40 60 80 100 1 2 3 4 V (kips) TEST WALL Theoretical and Experimental Shear Strength Theoretical Experimental Figure 7 – Graph of the difference between experimentally and theoretically determined shear friction strength in four wall samples Wall Name Theoretical (kips) Experimental (kips) Error % 1) UT -03 51 47 8.67 2) UT -04 87 82 6.01 3) Shing 8 48 49 2.84 4) Shing 6 49 50 7.76 Table 1 – Wall names corresponding to graph, theoretical and experimental shear friction strength values, and the percent error between them. • Shear friction is a governing failure mode in certain cases of reinforced masonry walls and the MSJC code should require it to be calculated for new buildings. • The new shear friction formula is relatively accurate in predicting the shear friction strength of a wall. • However, more testing and refinements must be done to make it more accurate. • NEES program Award No. CMMI-1208208 • NEES REU grant number EEC- 1263155 • NEES Operations award number CMMI-0927178 • Dr. B. Shing; mentor, provider of research for UCSD shake table tests and 2 theoretically tested wall samples • Andreas Koutras; mentor, provider of research for UCSD shake table tests • University of Texas; provider of 2 theoretically tested wall samples REFERENCES Masonry Standards Joint Committee. “Building Code Requirements and Specification for Masonry Structures.” 2013. Shing, Benson, et al. Improving Seismic Performance of Partially-Grouted Reinforced Masonry Buildings. 2014. OBJECTIVE The Masonry Standard Joint Committee (MSJC) does not currently require a calculation of a shear friction strength estimate. Therefore, new recommendations for accurate estimation of shear friction strength in a reinforced masonry wall are being formulated and evaluated with the aim of improving the MSJC code.