Experimental and Numerical Investigation of Load Bearing Capacity of Thinned End Precast Purlin Beams and Solution Proposals

Abstract

The construction sector in Turkey has met concrete prefabrication at the end of the 1960s. Prefabricated structures have been preferred more especially in industrial buildings due to their rapid production and fast erecting. The biggest disadvantage of these structures is the damages that occurred at especially the region of hinged connection. The connection of roof beams and purlin beams are generally assembled with a hinged connection. Therefore, a moment does not occur theoretically in the support areas and the cross-sectional effects of these beams are calculated as in simple support beams. However, since the shear force concentrated in the thinned end regions causes an increase in shear stresses, a number of special design rules are included in the relevant standards for the detailing of this region. Damages are observed in these connections as a result of snow accumulated on the roof especially after effective and prolonged snowfall. These damages pose a significant risk for thinned end beams, especially those in the relatively older prefabricated building stock. In this present study, the behavior of thinned end purlins under vertical loading, which have not been investigated extensively before, has been numerically and experimentally examined according to varying mechanical parameters. First, experiments of two purlin beam, which are in accordance with current standards and not, were carried out. Then another purlin beam in accordance with the standard, which was strengthened with carbon fiber reinforced polymer (CFRP) in order to prevent thinned end damage, was tested. Then, the results obtained from the purlins modeled with ABAQUS program were verified with the results of the experimental study. The results of numerical modeling were found to be very close to all experimental findings. The similarities between the damages observed in the experiments and numerical modeling showed that numerical models can be used in new parametric studies. After the verificifation, a number of parametric studies related to the mechanical properties of the purlins and strengthening alternatives were performed numerically. In the parametric study, concrete compressive strength, reinforcement tensile strength and the prestressing level used in the production of purlin beams, especially in existing purlin, was evaluated as a parameter with the idea that it may differ from the designed one. In addition, the behavior of purlins which are not in accordance with standards and strengthened with CFRP was also examined in the parametric study section. According to the results of the parametric study, it has been observed that a significant increase in shear capacity has been achieved with the increase of concrete and steel strength although the concrete compressive strength is more effective. The results showed that increasing the pretension value does not have a significant effect on the capacity. In addition, the shear capacity of purlin strengthened with CFRP has increased up to 50% and the damage has shifted to out of the thinned end region. With the aid of parametric study, different and feasible CFRP alternatives were also modeled and the best strengthening alternative was recommended. In addition, some suggestions for the design of the reinforcements for the thinned ended purlins were made.