Evaluation of Seismic Performance of Double-layer Steel Diagrid Systems

A new type of structural systems, called diagrid, has been introduced in recent years, in which the diagonal members are often located in the exterior frames while the interior frames, including vertical columns, resist only the gravity loads. A novel double-layer diagrid system is proposed in this study and the equations related to its lateral stiffness are extracted. The combination of angles of internal and external diagonals is also investigated to obtain the desired stiffness. Eventually, considering a 12-story structural model, the seismic performance of the proposed system is investigated and compared with conventional diagrid systems through changing the angle of diagonals in interior and exterior frames. Results show that double-layer diagrid systems are more suitable than conventional diagrid systems in providing stiffness and strength criteria. Moreover, a proper combination of internal and external angles improves the ductility, as well as increasing the amount of energy dissipated by the structure

Effect of Mixed Foundry Sand and Rice Hull Ash on the Mechanical Properties of Concrete

Waste foundry sand is the by-product of metal casting industry. Rice hull which is often burned after it is removed from rice is also a by-product of the agriculture industry. Disposing of these wastes leads to the environmental pollution. To optimal use of these wastes and avoid the adverse effects of dumping them, regular sand has been partially replaced with the waste foundry sand and rice hull ash pozzolan has been also used as a partial replacement for cement in making concrete. XRF, XRD and SEM experiments, compressive strength, tensile strength (Brazilian), flexural strength, modulus of elasticity and water absorption tests have been conducted. The results showed a slight decrease in compressive strength of samples in which regular sand was replaced with waste foundry sand by 15 percent; however, adding the rice hull ash to this mixture led to make a concrete comparable with control one. Also, using foundry sand in mix designs affects their physical performance. Moreover, the use of waste foundry sand in concrete is both economically and environmentally suitable