Cambridge Shake Table Results

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  • 1. The Experimental Seismic Testing of Hypar Shells by Daniel Balding (CTH) Fourth-year undergraduate project Group D, 2012/2013 "I hereby declare that, except where specifically indicated, the work submitted herein is my own original work."

2. The Experimental Seismic Testing of Hypar Shells Daniel Balding, St Catharines College 1 Table of Contents 1 Introduction........................................................................................................................2 Project Proposal...........................................................................................................21.1 Motivation for the Hypar Roof....................................................................................21.2 Motivation and Objective............................................................................................31.3 2 Hypar Roof Design ............................................................................................................3 Hypar Shape and Background.....................................................................................32.1 Current Uses of Hypar Roofs......................................................................................52.2 Previous Testing..........................................................................................................62.3 3 Procedure and Methodology..............................................................................................7 Materials to be used.....................................................................................................73.1 Shell Properties ...........................................................................................................83.2 Hypar Properties..........................................................................................................93.3 4 Materials testing.................................................................................................................9 Reinforcement Mesh ...................................................................................................94.1 Latex Modified Concrete ............................................................................................94.2 Fibreglass Mesh Reinforced Latex Modified Concrete ............................................104.3 Results.......................................................................................................................134.4 Implications for Full Structure ..................................................................................194.5 5 Hypar Test and Results....................................................................................................21 The Structure to be Built, Scaling and Post Loading of Structure ............................215.1 Construction ..............................................................................................................225.2 Experimental Equipment...........................................................................................255.3 Experimental Procedure............................................................................................265.4 Predictions.................................................................................................................285.5 Results.......................................................................................................................285.6 Discussion and Implications......................................................................................365.7 6 Conclusions......................................................................................................................41 General Implications of Research .............................................................................416.1 Specific Conclusions.................................................................................................426.2 Further Testing..........................................................................................................436.3 7 References........................................................................................................................44 8 Appendix..........................................................................................................................45 3. The Experimental Seismic Testing of Hypar Shells Daniel Balding, St Catharines College 2 1 Introduction Project Proposal1.1 TSC Global is a charity organisation that works to develop a sustainable form of housing in countries where living conditions are poor, either through the effects of a natural disaster or economic hardship. For several years now they have been utilising hypar roofs - whose name originates from the hyperbolic paraboloid shape of the surface - to provide the basis of this housing, however recent work in seismically active areas has prompted concern for the resilience of the structure to dynamic loading. For this reason it was decided to attempt to further determine the strength of the structure to help justify its continued use. Motivation for the Hypar Roof1.2 TSC Global promote the development ethic of roof first housing, and see this as the quickest and most sustainable method of delivering shelter to many in a short amount of time. This concept works by building simple roof structures and supporting them on basic corner posts, before any other building work takes place. This gives the inhabitants immediate shelter from rain and intense sun, and allows them to use local techniques to construct temporary and then permanent none load bearing wall structures as and when required. The desirable attributes of the roof can be linked directly to the conditions in which the structures are to be implemented. In general the economic climate will be poor - a key reason for the requirements of the houses - either through lack of state support or natural disaster. There will also be little or no construction equipment or training for the work force for similar reasons, thus requiring a simple, cheap and repeatable solution. Further to the local conditions, for the roof first method to be effective the roofs themselves must be quick to construct, as the key benefit is the speed at which shelter can be delivered. The structure must also be light, allowing for them to be constructed on the ground, and manually lifted onto simple, small foundation supports. Finally the roofs must be strong and durable to provide a protective and sustainable solution which must be a considerable improvement to living conditions before. The thin shelled hypar roof structure is a good fit to the above requirements with its simple construction sequence and use of readily available materials. 4. The Experimental Seismic Testing of Hypar Shells Daniel Balding, St Catharines College 3 Motivation and Objective1.3 TSC Global have utilised the hypar design in many projects around the world including cases of resettlement after natural disasters. A recent case of this is the resettlement of communities following the Haiti earthquake in 2010 and due to the nature of the disaster, further requirements of the construction were to have resilience to any future earthquakes. Whilst the original designers of the hypar roof claimed that the shell would perform well under dynamic loading, this has never been tested or quantified, and the failure mechanisms of the roof structure were unknown. The primary objective of this project is thus: To determine the resilience of a typical hypar roof to seismic loads, and to determine the failure modes of the structure when a critical dynamic load is reached. This will be done firstly by finding the material properties of key materials used in construction, including analysis of how the concrete shell of the structure could fail. A half scale hypar roof will then be excited using real earthquake records until failure occurs. Specific objectives are to: Identify typical failure mechanisms in the material used for the roofs shell Find what peak ground acceleration causes first and final failure of the hypar Identify the fundamental mode and frequency of the hypar Quantify the dangers faced to the structures inhabitants should an earthquake occur 2 Hypar Roof Design Hypar Shape and Background2.1 The word hypar was first used by Heino Engel in his 1967 book Structure Systems [1] and originates from the roofs shape a hyperbolic paraboloid which is formed when a square frame covered with a flexible fabric is twisted from two opposing sides. This results in a doubly curved surface, with parabolas being created in both diagonal directions. A specific property of the hypar shape is that a line on the surface of the fabric between equal points on two opposing edges of the structure will remain perfectly straight, regardless of the extent to which the frame is twisted. This can be seen in Figure 2.1 and allows the shape to be created 5. The Experimental Seismic Testing of Hypar Shells Daniel Balding, St Catharines College 4 by completely rigid members spanning in two directions a feature which is utilised in the construction of the structure. A typical roof is formed by four hypar surfaces constructed onto a square based frame creating a curved pyramid structure with side lengths ranging between three and eight metres. The first noted use of a structure based on the hyperbolic paraboloid was by Felix Candela, a Spanish Engineer who worked with concrete shell structures predominantly in Mexico in the 1950s [2]. His work on doubly curved surfaces or saddles was based on the principle of tension and compression cables and arches, removing the need for bending capacity in thin walled shells. Whilst this effect can be generated using a variety of shell shapes and geometries, it was identified by Candela that the hyperbolic paraboloid provided by far the easiest and most practical construction method. This is due to the straigh