Inverted roof - Jetwan Buddha Vihar

Introduction

The architecture firm Sp+a had designed a regular two slope roof with wooden understructure and thatch panel roof. As thatch roofs require a minimum slope of 45^o, the roof height at the centre became very high, which turned out to be the challenge. Hence thatch roof was ruled out. The solution was found in an inverted roof but had to be designed structurally from recycled wood. As the span was more reverse roof was continued with reclaimed Mangalore tiles.

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Hypothesis

Designing structurally and aesthetically, wooden understructures for inverted roof where the valley (Water channel) is in the center, using recycled wood, sourced from the ship breaking yard at Alang. 

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Experiment

• Based on a given brief, the basic design was to use rafters of certain length, number of supports with dimensions.
• 2 spans with three rafters were constructed for the experiment.

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Procedure

A truss was designed from required & available wooden section. To conduct the experiment, 3 trusses were made with all fixing details and then tested for assumed and designed dead load, live load and factor of safety as per the recommendation in code.

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Testing procedure

After installing the trusses, deflection was checked. Then apply uniformly distributed load on the roof. Gradually, the load was applied on the roof with sandbag and brick. Initially, 25% load was applied, which was increased to 50%, 75% and 100% and deflection was checked for respective loads. After 100% loading, the load was kept for 3 days to check for creeping deflection.

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Findings

The deflection noted during the testing procedure was under permissible limit of deflection. Hence the designed wooden truss performed well as per the conditions applied.

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