In-Plane Shear Resistance between the Rammed Earth Blocks with Simple Interventions: Experimentation and Finite Element Study

Abstract

The paper presents experimental and numerical works to assess the in-plane shear characteristics of rammed earth (RE) structures in Bhutan. The material characterization works involve compressive and tensile splitting strength tests on extracted cylindrical core samples. The effects of the RE layer thickness and drying period in the strength characteristics of the rammed earth is presented. The main experimental part reports in-plane shear tests on 3 test specimens, 1200 mm long, 1200 mm high, and 600 mm wide. The test matrix has unreinforced and reinforced specimens with variable RE layer thicknesses. For the reinforced RE specimen, the effectiveness of a simple intervention with insertion of reinforced concrete dowel at the RE block interface as a strengthening measure is discussed. Furthermore, corresponding finite element models were developed to verify the test observations. Both the experimental observations and numerical computations showed the effectiveness of proposed intervention technique in enhancing the shear strength and delaying the slip along the RE joint interface. The results showed that the shear strength of the reinforced specimen increased by 12.3% over the benchmark specimen.

Numerical Analysis of an Earthen Masonry Structure Subjected to Blast Loading

“…Mohr-Coulomb was adopted to model the sliding failure on the frictional interfaces between the contact elements. As the interaction does not work in the plasticity framework, the model assumes non-associative flow, and the dilatancy angle in the model was automatically assigned a value of 0, in line with work by previous authors [43,44]. The cohesion was considered negligible for this problem because the cohesion using the Mohr-Coulomb failure criterion cannot be modeled in Abaqus.…”

“…The cohesion was considered negligible for this problem because the cohesion using the Mohr-Coulomb failure criterion cannot be modeled in Abaqus. The normal stiffness and tangent stiffness (Table 3) were based on past studies [43]. Using the joint stiffness, the Young's modulus of the blocks was recalculated based on [45].…”

Strengthening Strategies for Existing Rammed Earth Walls Subjected to Out-of-Plane Loading

“…The unreinforced rammed earth (U-RE) represented a typical house built without any seismic components, and it served as the reference wall, while the rammed earth wall strengthened with a mesh and timber frame were aimed at retrofitting existing buildings. The details of the adopted specimen are presented in Figure 1, and Figure 2 illustrates the grain size distribution of the soil used [5]. All specimens were constructed on top of a rubble masonry foundation of 600 mm height and 600 mm thickness by local Bhutanese craftsmen following the traditional construction procedures practiced in the region to realize the actual behavior of such structures.…”

“…The available literature on rammed earth wall is rich in studies on in-plane loading [2][3][4][5][6][7][8][9]; however, only a few have discussed out-of-plane behavior [10][11][12][13][14][15][16][17]. Further, studies have been carried out exploring strengthening measures to improve the seismic performance of existing rammed earth structures by using flax fiber reinforcement [18], polyester fabric strips [9], cement mortar-steel fiber reinforcement [19], mesh composite [20], and canvas and tarpaulin as externally bonded fibers [3].…”

“…Although strengthening works were carried out for undamaged wall, this method was largely aimed at improving the strength of existing rammed earth walls in an out-of-plane direction. This work is an extension of the authors' previous works [5,[12][13][14]20,24], which largely focused on numerical modelling, reinforced RE with reinforced dowels and wedges, floor anchorage system, and mesh-wrapped strengthening on reduced-scale walls. The present study aimed to evaluate the feasibility and effectiveness of the two proposed strengthening techniques, which could be adopted in retrofitting the rammed earth buildings in Bhutan.…”