Lateral behavior of steel frames with discretely connected precast concrete infill panels

Abstract

As an alternative to the conventional structures for tall buildings, a hybrid lateral load resisting structure has been designed at Eindhoven University of Technology. It consists of discretely connected precast concrete panels with window openings in steel frames, and is a new application in infilled frames. Besides the structural advantages of hybrid construction, this structure offers an alternative construction method, improving the constructability of tall buildings. This will result in more economical and high quality buildings. The infilled frame is a type of structure that has proven to be effective and efficient in bracing low-rise and medium-rise buildings to resist in-plane lateral loads. It acts by composite action between the infill and its surrounding frame. Structural interaction between the two components produces a composite structure with a complicated behavior due to the fact that the frame and the infill mutually affect each other. Since the early fifties extensive research has been done into the composite behavior of infilled frames with masonry and cast-in-place concrete infills without openings. However, the application of discretely connected concrete panels with openings as bracing elements in steel frame structures has not been performed yet and represents a new area of research in infilled frames. The main objective of this investigation is to develop practical universally applicable design models for infilled steel frames with discretely connected precast concrete panels, allowing for an accurate prediction of the strength, stiffness and deformation capacity of this type of structure. In order to develop these design models, the structure has been subjected to experimental, numerical and analytical investigation. First, full-scale tests on single-storey, single-bay infilled frame structures were carried out. Objectives of this experimental study were to observe the general behavior of the infilled frame in terms of stiffness, strength and failure modes. In addition, experiments were performed on components of the discrete panel-to-frame connection. Subsequently, finite element models were developed and validated by simulating the experiments. For this purpose, finite element analyses taking non-linear material and structural behavior into account were performed. It has been shown that the finite element model developed for the overall infilled frame behavior can be used to predict the lateral load versus deflection relationship and the ultimate lateral load with good accuracy. Accordingly, the validated finite element model has been used to carry out a parameter study to investigate various configurations of the infilled frame. Four parameters have been studied with respect to their influence on the structural response. These parameters are the frame member dimensions, the rotational stiffness of the frame joints, the infilled frame aspect ratio and the panel opening geometry. From the simulated load-deformation curves, structural characteristics have been derived. These have served as a verification for the developed analytical models for the prediction of the lateral stiffness, the ultimate lateral load and deformation capacity of the structure under consideration. The analytical models are based on the concept of the equivalent diagonal strut, considering the structure as an equivalent braced frame system with a compression diagonal replacing the infill. Finally, a practical method for designing steel frames with discretely connected precast concrete infill panels has been proposed. The aim of this method is to get a good prediction of the internal forces and the lateral deflection in the preliminary phase of the design, without the use of advanced computer simulations. The design method provides a useful guideline that a design engineer can follow, in order to design building structures consisting of steel frames with discretely connected precast concrete infill panels, resulting in a ductile structure, possessing both adequate strength and stiffness.