Energy dissipating facade systems designed to reduce structural response during earthquakes

Abstract

Strong earthquakes cause severe shaking, mostly lateral, of the ground over a large area which imparts strong excitation to building structures. These earthquakes are extreme actions, from which buildings may not survive unless being properly designed in advance. In recent years, many new devices such as energy-absorber or isolation systems have been introduced. But, most of them have some disadvantages such as complexity of design and requirement of large spaces for installation and significant cost. To date the engineering community has seen structural facade systems as non-structural elements with a high aesthetic value and a barrier between the outdoor and indoor environments. As an integral part of buildings, they are susceptible to potential failure when subjected to severe environmental forces such as earthquake and high wind in case they are not designed properly. Seismic loads can potentially impose significant in-plane loading on the facade system and may lead to damage and breakage in the case of insufficient connection detailing and big inter-storey drifts. The role of facades in reducing energy use in a building has also been recognized and the industry is witnessing the emergence of many energy efficient facade systems. Despite these advancements, the facade has been rarely considered or designed as a potential earthquake-induced vibration absorber for structural buildings. Development and implementation of advanced facade systems for enhancing the seismic response of building structures have been a topic of debate for structural and architectural engineers for some time. The main idea here is to design and implement a seismic control method using a novel façade system, as an energy-absorbing device, to decrease the level of energy imparted to the main structure during seismic activities and hence reliance structural ductility to dissipate seismic energy. Various configurations and specifications of the proposed system are suggested in this thesis. Multiple design variations were evaluated as well. To prove the concept and find the optimum value of façade damper properties, a series of non-linear structural analysis and finite element modelling was conducted using SAP2000 and ANSYS program respectively. First, conventional façade brackets were replaced by the so-called sacrificial elements, which can have back and forth movements during earthquake excitations. Predefined plastic hinge behaviour is suggested for the façade bracket elements in a double skin façade system. Second, façade bracket properties in terms of stiffness and damping of the proposed system were optimized to obtain the desired response. Third, the potential of utilizing a movable exterior skin in a double-skin facade was investigated and it was found that with optimal allowance of façade in-plane movement and appropriate bracket stiffness, a substantial portion of earthquake-induced vibration energy can be dissipated, which could lead to avoiding expensive seismic designs. A series of dynamic time history analyses were carried out to determine the behaviour and response of the proposed system on typical concrete frame structures under different intensity earthquakes. SAP2000 and ANSYS programs were used for the numerical analyses in all phases of the feasibility study. The initial works demonstrated that the seismic response for low- and mid-rise structural buildings subjected to moderate to severe earthquakes can substantially be reduced by the introduction of a smart design of a double skin system. Application of flexible connections in façade systems can, if properly designed, reduce the inelastic deformation of structural models in comparison with the case without flexible connections.

Date of Award	2017
Original language	English