Effects of Mechanical Bar Splices on Seismic Performance of Reinforced Concrete Buildings

Mechanical bar splices, which are commonly referred to as couplers, are currently used in reinforced concrete structures to directly connect steel bars in lieu of conventional lap splicing. With proper detailing, couplers can be utilized to connect precast beams and columns to accelerate the construction. However, the experimental and analytical studies regarding their effect on the performance of RC moment-resisting frames (MRFs) are scarce. Current ACI 318 restricts the use of couplers in plastic hinge regions of special moment-resisting frames (SMRFs). Nevertheless, they can be incorporated at any location of the intermediate and ordinary MRFs. The seismic performance of RC frames incorporating mechanical bar splices in plastic hinge regions was analytically investigated in the present study. Ordinary, intermediate, and special moment-resisting frames (OMRF, IMRF, and SMRF) were included in the study. Three-, six-, and nine-story buildings were designed for each frame type (nine frames in total) according to current ASCE 7 and ACI 318 codes. Modeling methods were proposed for mechanically spliced RC members then the results were verified against large-scale test data from literature. Subsequently, more than 100 pushover analyses were performed on the nine frames by varying the coupler rigid length factor and the coupler length. The results showed that the coupler length, the coupler rigidity, the height and the type of frames affect the displacement capacity of mechanically RC frames. Long and rigid couplers may reduce the displacement capacity of a short SMRF up to 42%. A simple design equation was proposed to quantify the effect of mechanical bar splices on the displacement capacity of RC frames

Effects of Plastering and Ferrocement on the Shear Properties of Masonry Triplets

Masonry triplet is formed by three and half bricks keeping the same type of bond exhibited in a brick wall.  The triplet has been investigated by researchers as an indicator of lateral loading capacity of masonry wall.  Although strength is an important parameter in determining the property of triplet, displacement capacity is significant specially for the cases of lateral loads such as wind load or earthquake load.  Experimental investigations carried out to determine the effect of plastering and ferrocement in masonry triplets in terms of both shear strength and strain at maximum stress.  The study identified several parameters that affect these properties e.g. mortar strength, mortar thickness, compressive strength of brick, plastering layer thickness, diameter of the wire mesh, and amount of wire mesh.  Equations have been proposed to determine the shear strength and strain at maximum stress of the triplet based on these factors.  Bond strength was found to be the key factor for the failure of the triplets.  It can be inferred that the construction in Bangladesh lack the bond strength in the horizontal bed surface, decreasing both the load and displacement capacity of the brick wall.  Ferrocement can be used as a retrofitting technique as it has been found from the tests that laminating the triplet surface with ferrocement prevents sudden collapse and confines the triplet so that the shear strength and strain at maximum stress increase.