Study the Behaviour of Precast Portal Frame under Lateral Loading

Abstract

Precast concrete is significantly being used as earthquake resisting structures in many parts of the world. Earlier, due to the lack of understanding of the basic nature of seismic behaviour, the precast concrete structures were viewed with scepticism in seismic regions. Significant structural damage to concrete frame buildings and precast structures has been observed during moderate to large earthquake that have occurred from 1960 to 1999.The poor behaviour of precast concrete building structures during earthquakes are due to the improper design and detailing of ductile element, inadequate diaphragm action, poor joint and connection details, inadequate separation of non-structural elements and inadequate separation between structures. It is important to study behaviour of Precast Connection under lateral load since slender and flexible structures are sensitive to lateral load. The present work mainly deals with the study to understand the behaviour of Portal frame with different types of connections between precast elements under lateral load. Experiments are conducted on four specimens, one portal frame with monolithic connection and three portal frames with precast connections, under lateral loading. In this study, Different types of dry precast connections between beam and columns are considered to construct precast portal frame. The portal frame is a part of the workshop building having 9 m span of 4.5 m height. The spacing between portal frames is 4 m c/c. Three different types of dry precast connections at beam-column junction are considered for experimental study. Typical specimen is having one beam and two columns. Based on dimensional analysis 1/3rd scale specimen of portal frame are cast. Fixity of the column is very important for the testing under lateral loading. For achieving fixed base condition, reinforcement cage of the column is welded with the 12mm thick steel plate further this base plate is connected to the base box assembly using 16 mm diameter bolts. Load is applied laterally at the top of frame using hydraulic jack. Experimental results in terms of horizontal displacement of portal frame at different height of column, vertical displacement at different location of beam and strain are measured at different interval of loads. For measurement of load, load cell is attached with hydraulic jack, and for measurement of displacements LVDT and dial gauges are used. Strain in reinforcement and Strain in concrete are also measured at critical location of the portal frame using electrical resistant strain gauge. Data acquisition system is used to collect all digital data for further analysis. Behaviour of specimens is presented through load-displacement, load-strain relationships and failure pattern. Based on experimental study, Portal frame with dowel bar connection between precast elements behave similar to monolithic portal frame. It shows higher load carrying capacity but presents ductile behaviour under lateral loading. Portal frame with seated connection between precast elements behave similar to monolithic portal frame. It shows singly less load carrying capacity but presents ductile behaviour under lateral loading. Portal frame with corbel connection between precast elements shows less lateral load carrying capacity but is capable of resisting lager deflection compared to monolithic frame.