Keywords: repair, strengthening, coupling slabs, reinforced concrete, structures.

This paper is concerned with the response of repair strengthening of slabs used to effect the coupling of shear walls. An experimental investigation of 1/2 scale reinforced concrete shear wall slab model is described. Based on the results of the model, an analytical simulation is used to investigate the response of planar coupled shear walls before and after repair of joints slabs to shear walls at the elasto-plastic case. The elasto-plastic condition is restricted to the connecting slabs using a convenient perfectly elastic/perfectly plastic material model. In addition, the work presents results obtained with the discrete force method and discusses its applicability to some representative problems.

In high multi-storey, reinforced concrete buildings coupled shear walls (CSWs) can provide an efficient structural system to resist horizontal forces due to wind and seismic effects. CSWs are usually built over the whole height of the building and are laid out either as a series of walls coupled by beams and/or slabs or as a central core structure with openings to accommodate doors, elevator wells, windows and corridors. The shear walls resist the external loading by cantilever bending action, which results in rotations of the wall cross-sections. The floor slab is then forced to rotate and bend out of plane where it connects rigidly to the walls. Due to the large depth of the wall, considerable differential shearing action is imposed on the slab, which develops transverse reactions to resist the wall deformations and induces tensile and compressive axial forces into the walls.

Both theoretical and experimental studies have shown that the main coupling action takes place in the corridor area, and high stress concentrations occur around the inner edges of the shear walls. These high stresses may lead to local cracking of the concrete, with yielding of the reinforcing steel, causing a significant reduction in the coupling stiffness, since flexural resistance is lost at the most effective part of the slab. Cracking, on the other hand, will cause a redistribution of stresses to other parts of the slab, and bring into active participation for the loss of stiffness at the crack A small number of experimental investigations have analysed the influence of cracking on the effective stiffness of slabs subjected to either monotonic or cyclic loading. These have shown that a considerable loss of stiffness occurs because of cracking, amounting to a reduction of 60 provided by experimental investigation a related numerical study was made to analyse coupled shear walls systems with an effective width using the discrete force method.

Repair and strengthening of such slabs to their original form is essential in multi- storey buildings. In recent years, the repair of existing structures has been amongst the most important challenges in civil engineering. The process of repair design and specification consists of determining the exact function of the repair so that the correct repair technique and materials can be specified[1,2,3]. Various materials and methods are available for strengthening purposes. One way to repair or strengthen concrete structures is by adding reinforcement either surface embedded or in drilled holes. Another kind of external reinforcement is plate bonding. Plates made of steel, fibre reinforced plastics, and carbon fibre reinforced polymers can be used. These materials offer the engineer an outstanding combination of properties, such as low weight (making them much easier to handle on site), immunity to corrosion, excellent mechanical strength and stiffness, and the ability of formation in very long lengths, thus eliminating the need for lapping at joints. Other important reasons for strengthening of the structures include, upgrading of resistance to withstand underestimated loads: increasing the load-carrying capacity; eliminating premature failure due to inadequate detailing. An analytical simulation is used to investigate the effect of the building response before and after repair based on experimental tests. The resin injection and fiber reinforced plastic was used as strengthening materials between joint slab to shear wall. In this study, the discrete force method is employed for the analysis[4].

1

Nadjai, A., Johnson D., Abu-Tair, AI., "Behaviour of coupled shear walls having repaired coupling beams", International Congress, Creating with Concrete, Dundee, Scotland, 323-331, 1999.

2

Abu-Tair, A.I., Nadjai A., Gross, M., and Cousins, W., "Performance of epoxy repair and plate bonded shear wall coupling beam joints damaged by earthquake", International Congress, Creating with Concrete, Dundee, Scotland, 687-699, 1999.

3

Kay, E.A., "The European standard on concrete repair principles", Construction Repairs: Concrete Repairs 6, (11), 52-55, 1997.

4

Nadjai, A., Johnson, D., "Elastic and elasto-plastic analysis of planar coupled shear walls with flexible bases", Int. J. of Computers & Structures, (68), 213- 229, 1998. doi:10.1016/S0045-7949(98)00036-4

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