Experimental Behaviour of simple Bolted shear Connections in Steel Plates after high Temperatures

Abstract

ABSTRACT Steel is widely used materials due to many advantages. It offers over other construction materials. These include high strength, ductility, ease of fabrication, and speed of construction. Steel joints are a major part of steel structures; it is responsible for the transmission of loads such as shearing, tension and bending and the stability of the building. The high temperature affects the mechanical properties of the steel. Therefore, the connections are considered as one of the affected parts if the building was exposed to fire. To maintain the safety of the building, there is a need to know the behaviour of the joint after exposure to high temperatures. This study deals with the effect of high temperatures on the mechanical properties of thin steel carbon plates (2mm , 4mm), and its behaviour in bolted connections after the fire. The experimental work includes testing of thin carbon steel plate bolted connections and coupons. They were exposed to a high temperature to simulate fire conditions, at different temperatures 400°C, 700°C, and 1000°C, in different durations time(30,60,90,120 min), and cooled in water or air. The specimens and coupons were tested in a tensile. The coupons were used to find the mechanical properties (yield stress, ultimate stress, and modulus of elasticity). The specimens were used to find the ultimate load, ii type of failure, axial displacement, and transverse displacement (curling). The results showed that after the steel was exposed to high temperatures there is a reduction in the thickness. The yield stress, ultimate stress, and modulus of elasticity for heated coupons dropped with increasing the duration of heating with cooled in air. The curling failure caused a reduction in the ultimate load when specimens of 2 mm thickness heated to 700 ºC and 1000 ºC and cooled in air. The ultimate stress for heated coupons drops with increasing the duration of heating to 400 ºC, 700 ºC, and 1000 ºC. For coupons of 2mm and 4mm thickness, it dropped by 10%, 13% and 14% and 4%, 11%, and 15% respectively after 120 minutes of heating and cooling in air. The load-carrying capacity of the bolted connections can increase with increasing the heating temperature to 700 ºC and 1000 ºC for specimens of 2mm thickness by 1% and14 % respectively after 120 minutes of heating and cooling in water. For the 4mm specimens, it improved in 400 ºC, 700 ºC and 1000 ºC by 2%,10%, and 9% respectively after 120 minutes of heating and cooling in water. To maintain the strength after the event of a fire in the steel structure buildings, it is recommended to use water to extinguish the fire to maintain the strength in the parts of the structure