A Concept for Fixing "Heavy" Facades in Seismic Zones

Abstract eng:
So called “heavy” façades with a dead load of more than 100 kg/m² are usually constructed in brickwork, natural stone cladding or using concrete panels. Load bearing steel anchors are used to transfer the load to the main load bearing sub-structure. According to current standards, façades are defined as non-structural elements. Previously, the calculation of these anchors only assumed static loads such as dead-loads, wind loads and constraining forces. In countries with seismic risk the façade’s seismic load can be replaced using a static equivalent load acting in a horizontal unfavorable direction. Façade components must be appropriately designed to prevent unintentional tipping (tilting), falling or from hitting other elements; including swaying of components on hoist or tearing of pipes. On the one hand, the intention is to prevent physical injuries during an earthquake, and on the other hand to ensure that rescue operations after an earthquake are not hindered by fallen or falling façade segments. Current design practice (e.g. numerical simulations) assumes that façade constructions are a mass fixed to a building with zero stiffness. However, seismic design should not only focus on the load bearing structure; in fact there is significant interaction between main structures and façades, which can seriously influence the bearing behaviour of the whole structure. Experience with earthquake damage to building-façades, which are fixed according to current standard solutions, illustrate clearly that this concept does not work properly. Cladding panels fastened to a building are part of the whole structural system; these provoke a seismic response with the main sub-structure. The higher stiffness of this “resistance system” results in forces that are greater than those calculated based on frame models. Therefore the panels themselves have to be dimensioned according to these resulting stresses and the anchors have to be designed accordingly. Fixings should be designed according to these assumptions. They form the link between the two systems (façade / load bearing structure) and have to be adequately dimensioned. It also has to be examined whether the fixings should be designed as ductile or rigid; this influences the interaction significantly. In general, new methods for modeling the behavior of heavy façades during earthquakes need to be developed. Suitable recommendations are illustrated in this paper. Results from shake table tests support this technical approach. Additional shake table tests were provided to compare rigid and ductile (load) bearing behavior of fixings for heavy façades. This paper provides an overview of the calculation methods and test methods. Shake table tests are used to show the (load) bearing behavior of the system structure/façade. The technical background is explained and the experiment results are illustrated.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket