Behavior of Masonry Walls Constructed Using Locally Available Dry-Stack Interlocking Masonry Units

Abstract

Masonry is one of the oldest construction materials. But there are several disadvantages of using masonry such as time consuming, need highly skilled laborers, the amount of mortar that is required to be mixed on-site andShrinkage crackingdue to mortar. Dry-stacking masonry is a suggested method to minimize some of these disadvantages. Dry-stacked masonry is manufactured as traditional brick work but without mortar joints. The dry-stack method makes construction significantly easier and thus reduces the need for skilled labor.However, dry-stack systems are not without their disadvantages such irregularities in the individual blocks and high initial settlement. Although the worldwide interest for the dry-stack masonry construction technique because of its attractive advantages, the lack of knowledge of loading and deformation behavior of dry-stacked masonry structures exists up to now in contrast to this of mortar layered brickwork.There are many available systems of interlocked mortar-less structures are already available in the local and worldwide markets. But these systems are based only on a small number of observations on the specific structures without gaining general information. Therefore, these systems are very restricted in design and application. The main objective of this research is to investigate the in-plane behavior of locally available dry-stacked masonry systems in Egypt, (i.e. Azar and Spar-lock systems) and comparing between these two systems and traditional masonry blocks system and study the feasibility of using locally available post-tension technique in dry-stacked masonry systems to improve the in-plane performance and reduce the grout used in dry-stacked masonry constructions. To meet these objectives, experimental and analytical studies were conducted and documented in the thesis. In order to design the test program, properties of all used material were investigated then a pre-test analysis was carries out to predict the ultimate load carrying capacity and failure mechanism and choose how to construct sliding control to fulfill the design requirements. To assess the in-plane behavior of dry-stack shear walls, ninefull-scale masonry shear walls were constructed and tested under in-plane cyclic loading. The specimens were constructed using three different concrete blocks, with different parameters such as grouting, reinforcement, post-tension and sliding control. The test results of each wall were presented in the form of crack patterns, load-drift angle curve, flexural strain at expected critical sections, panel drift angle and post-tension force - drift angle curves. Parametric study using finite element modeling was performed to cover those parameters which were not considered in the experimental study such as position of post-tension bars and its initial stress. Conclusions The following conclusions were drawn from the experimental and analytical studies carried out in this research: (a) General Behavior The dry-stacked Azar system behavior resembles the conventional masonry system and can be designed with the same formulas for grouted, un-grouted, reinforced, and post-tensioned walls. Even the Spar-lock have special and better interlocking system than other dry-stack systems but it prevents the inclusion of horizontal reinforcement, thus leading to low ultimate load. The Spar-lock system can be rearranged to allow horizontal reinforcement in the face shells which improves the ultimate load capacity by 17.90%, but the end blocks can’t be reinforced. The use of post-tensioning with conventional and Azar walls can be an economical solution that can reduce the cost of the main reinforcement, grouting and skilled mason. The un-grouted post-tensioned dry-stacked masonry shear walls can resist more than 62.00% of the ultimate load capacity of the reinforced fully-grouted conventional walls. The open/close movement of dry-stack joints could delay the crack propagation through the wall, the first crack would be observed at about 0.59% drift. The sliding control improves the dry-sacked shear wall maximum drift up to 1.56% by allowing the wall to slide along the base. For Azar and conventional block walls, the concentrated flexural rotation at wall footing was the main contribution of lateral displacement for reinforced and post-tension grouted walls, while the un-grouted post-tension walls had reasonable panel distortion contribution about 47% due to the open/close movement of dry-stack joints. The sliding control could enlarge the sliding contribution up to 35%. The average residual displacementsare 59% and 37% of the maximum displacements for conventionally reinforced and the post-tensioned walls respectively. The post-tensioning with sliding controlcould reduce the residual displacement in dry-stack wallsto 10.9% of its overall drift. Unexpected failures could be occurred due to stress concentration as a result of irregularities of individual dry-stack blocks. The designing equations proposed by MSJC (2008) for reinforced and post-tensioned shear walls provides a good estimate for lateral load capacity with about 15% variation. The proposedformulas for post-tension shear walls is given as following: M_u=(f_ps A_ps+f_y A_s+P_u )(d-a/2) Where, a=(f_ps A_ps+f_y A_s+P_u)/(0.80f_m^/ b)