Static And Dynamic Behaviour Of Cement Stabilised Rammed Earth Panels And Building Models

Abstract

Rammed earth is one of the earliest building materials used for structural walls. Stabilised rammed earth is a variant of traditional or pure rammed earth that involves addition of a small amount of cement to improve strength and durability. Rammed earth buildings experience in-plane shear forces as well as flexural stresses due to out-of-plane bending especially during earthquakes. The thesis attempts to examine the behaviour of cement stabilised rammed earth wall elements and building models subjected to lateral loads. A brief introduction to rammed earth construction followed by a review of literature on rammed earth and details of the existing codes of practice on rammed earth is provided in Chapter 1. Chapter 2 deals with the flexural strength, modulus of rupture, stress-strain relationships and free vibration characteristics of cement stabilised rammed earth (CSRE) in greater detail. Properties of raw materials used in the experimental investigations followed by a detailed description of the experimental programme, method of preparation of various types of specimens and their testing procedures are provided. Flexure strength and modulus of rupture were determined in both the orthogonal directions. Influence of (a) thickness of the specimen, (b) direction of compacted layers with respect to the flexural tension developed and (c) effect of cement slurry coating between the compacted layers on the flexural strength of CSRE were examined. The investigations show that flexure strength increases with the increase in the specimen thickness and a coat cement slurry on the compacted layers leads to improvement in flexure strength. The flexural strength parallel to compacted layers is higher when compared to flexure strength perpendicular to compacted layers. Stress-strain relationships show that the initial tangent modulus of CSRE in saturated condition is about 60% of that in dry condition. Damping ratio as obtained from the free vibration studies is found to be 0.022 in the two orthogonal directions. Dynamic characteristics of CSRE building models are presented in Chapter 3. A simple alternative to shake table called as “Shock Table” was used in the present investigation for providing base motion to the building model. A half-scale CSRE building model with R.C lintels only above door and window openings (with no earthquake resistant features) was constructed on the Shock Table. The wall thickness of the building model was 100 mm. Procedure for construction, instrumentation and testing of the CSRE building model is presented. Responses measured and damages observed are discussed in detail. Finite element (FE) analyses were performed on six different building models with different earthquake resistant features using commercially available FE software (NISA V17). Both free vibration and forced vibration analyses were performed. Natural frequencies and forced vibration responses (acceleration) of building model (BM1) obtained from experiment and FE analysis were compared. Responses (free vibration and forced vibration) of other five building models were predicted using FE analysis. Crack patterns of the building models with roof and without roof are compared. The thesis ends with a summary of the results and concluding remarks in Chapter 4.