Study of the Behavior of Precast Connections for Precast Portal Frame subjected to Lateral Loading

Abstract

Precast construction is increased in recent past because of many advantages of the precast technology over conventional cast-in-situ construction such as better quality, rapid construction, lesser requirement of skilled labours at site etc. The main concept of precast construction is that all the components of structure are produced in controlled environment and it is being transported to the site and later erection work is carried out at site. In precast structure, connections between precast elements are important element to transfer force from one element to another element. In past, it was observed that, major collapse of precast structures took place because of failure of connections between precast elements. Therefore, it is important to study the behavior of connections between various precast elements.

In this study, behavior of the precast connections provided away from the beam-column junction in portal frame is evaluated through experimental studies under monotonic lateral loading. Experiments are conducted on reduced 1/3rd scale specimens of portal frame, which is extracted from assembly hall building having overall plan dimensions 16 meter × 6 meter with 4 meter c/c spacing between portal frames. Experimental studies are conducted on one monolithic portal frame and three precast portal frame having different connection detailing. Connections are provided at three locations in the portal frame i.e. at mid height of columns and at mid-span of beam. Out of three precast portal frame, two frame are constructed by providing wet connections and one frame is constructed by providing dry connection. In wet connections, reinforcement bars projecting from individual precast elements are connected by overlapping or welding of reinforcement and subsequently empty space of connection region is filled with cast-in-place micro concrete. In dry connection, individual precast elements are connected through welding of steel plates.

A monotonic lateral load is applied at the beam level through hydraulic jack of 100 kN capacity during experimental studies. Response of test specimens are measured in terms of ultimate load carrying capacity, ultimate lateral displacement, deflection profile of columns, strain measurement on concrete surface at selected location, crack formation and failure pattern. For measurement of load, load cell is attached with hydraulic jack and for measurement of displacements LVDTs and dial gauges are used. Strain at selected location on concrete surface is also measured using electrical resistant strain gauges. Data acquisition system is used to collect the responses for further processing.

The results of this experimental study shows almost similar behavior of precast portal frames and monolithic portal frame in terms of crack formation and failure pattern. Ultimate load carrying capacity and lateral deflection are maximum for precast portal frame having dry connection as compared to other portal frames. For precast portal frames, any significant failure is not observed within connection region, which indicates that, forces are effectively transferred from one element to another element through connection.