Recycling of building waste has become essential process in the construction industry due to the sustainability and economic benefits such as decreasing the waste to landfill, conserving natural resources, and reducing pollution. Large amount of building waste is produced from the construction and demolition process of reinforced concrete (RC) structures. In this paper, the effect of using recycled coarse aggregate (RCA) on the behavior of concrete is experimentally studied. The RCA is prepared by crushing and sieving of waste of standard compression test cubes having a compressive strength ranging between 25 MPa and 30 MPa. The physical and mechanical properties of RCA are experimentally estimated and compared to those of natural coarse aggregate (NCA). A set of 72 standard concrete cubes, cylinders, and beams specimens are made using coarse aggregate replacement ratios (CARR) of 0%, 30%, 50%, and 100%. The specimens are tested to estimate the compressive, splitting, and flexure strengthens at the ages of 7 and 28 days. The study is extended by using the RCA in casting 12 RC columns with CARR similar to those of specimens. The columns are tested in an axial compression test protocol till failure. Crack patterns, failure loads, strains, displacements, and toughness of the tested columns are compared. It is concluded that using a CARR of 30% and 50% and a specific water cement ratio provides better mechanical behavior than that of NCA while the CARR of 100% yields worst mechanical behavior compared to that of NCA.

Wide beams are commonly used in reinforced concrete (RC) structures for architectural considerations such as facilitating the placement of services and providing adequate clear height. However, behaviour of these beams is not as efficient as normal width beams due to the small structural depth. Motivated by the lack of guidelines for wide RC beams with spiral reinforcement, this paper investigates their shear behaviour using innovative lateral reinforcement configurations. A comprehensive experimental program was conducted by testing nine beams under four-point loading. The effect of different parameters on the behaviour of such beams was investigated. These parameters included number, dimensions, and configurations of spirals. The experimental program also included testing of 18 standard cylinders spirally reinforced under compression to study the performance of confined concrete in the compression zone of wide beams. The results showed that the spiral lateral reinforcement is an efficient alternative for traditional closed stirrups for shear resistance in wide beams. Compared to regular closed stirrups, using spiral reinforcement or inclined links with regular closed stirrups can greatly improve the shear capacity and deformation. Also, reduction in the amount of lateral reinforcement can be achieved if the proposed lateral reinforcement is adopted instead of traditional stirrups. Based on the test results and the ACI 318–19 code, an equation is proposed and validated to estimate the shear strength of wide beams with regular/spiral lateral reinforcement.

Selecting appropriate structural system for reinforced concrete (RC) buildings is essential in the design process to satisfy serviceability and strength requirements. Using ordinary analysis (OA) may result in inaccurate estimation of differential shortenings (DS) between vertical supporting elements which might lead to structural and architectural problems. Efficiency of staged analysis including time-dependent effects (SAT) has been recently recognized for the analysis of these buildings due to considering the sequential nature of construction. In this research, eight RC buildings with heights ranging between 35 and 175 m and various structural systems, namely rigid frames (RF), shear walls (SW), wall frames (WF), and tube in tube (TT), are analyzed. An assessment is conducted for the adequacy of three mitigation alternatives to decrease changes between DS estimated using OA and SAT. In Alternative 1, cross sections of all vertical elements (columns and shear walls) are increased by 50%. Alternative 2 is performed by iteratively proportioning the dimensions of internal columns without changing the cross sections of edge and corner vertical elements. One outrigger system is introduced along the height of buildings with WF and TT systems in Alternative 3. Analysis of the eight buildings is implemented by developing a numerical model considering the construction stages and time-dependent effects. The alternatives assessment is conducted by comparing differential displacements (DD), bending moments, and shearing forces before and after mitigation obtained from OA and SAT. The numerical results showed that Alternative 1 is not efficient in mitigating the differences between the OA and SAT for all the studied buildings. However, an optimum solution can be achieved using the Alternative 2 for all investigated systems. Also, Alternative 3 was found adequate in partially mitigating the differences between the two analyses for the buildings with WF and TT systems.