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3.a Reinforced Concrete

Preliminary observations from biaxial testing of a two-storey, two-by-one bay, reinforced concrete slotted beam superassembly

C.A. Muir, S. Pampanin & D.K. Bull

Displacement incompatibility between reinforced concrete moment frames and precast flooring systems has been shown experimentally, and in historical earthquakes, to be an area of concern. Plastic hinge formation necessitates beam damage and the resulting elongation of the beam reduces the seating length of the floor, exacerbates the floor damage and induces unanticipated force distributions in the system. In severe cases this can lead to collapse. The slotted beam is a detail that protects the integrity of the floor diaphragm, respects the hierarchy of strengths intended by the designer and sustains less damage. The detail provides the same ductility and moment resistance as traditional details, whilst exhibiting improved structural performance. This is achieved with only a subtle change in the detailing and no increase in build cost.

This paper briefly presents the development of the slotted beam in reinforced concrete. The design and construction of a large scale reinforced concrete slotted beam superassembly is described. The experimental method used to undertake biaxial quasi-static testing in introduced.

Preliminary observations from the experiment are presented. It is shown that the reinforced concrete slotted beam is a viable replacement for the traditional monolithic detail. Extremely promising structural performance and significantly reduced damage compared to monolithic reinforced concrete details is presented.

[Paper 024]

Wall-to-floor interaction in concrete buildings with rocking wall systems

R.S. Henry, J.M. Ingham & S. Sritharan

Previous research has shown that rocking or self-centering precast concrete walls provides superior seismic resistance when compared to traditional concrete construction. However, uplift at the base of the wall causes a vertical displacement incompatibility between the wall and floor diaphragms. The type of wall-to-floor connection and the floor diaphragm's resistance to wall uplift can have a significant influence on the seismic behaviour of both the wall and the building. Finite element modelling indicated that the lateral strength of a building is significantly increased when the floor diaphragms are rigidly restrained to the rocking wall. Additionally, reparable damage is caused to the floor slab when a cast-in-place connection is detailed. An alternative to a rigid cast-in-place connection is to use a wall-to-floor connection that will isolate the floor from the vertical displacement and rotation of the wall, preventing any significant floor damage. The influence of the wall-to-floor interaction on the seismic response of a building is not limited to rocking walls, and has the potential to be more severe for traditional reinforced concrete walls, increasing the vulnerability of the wall to shear or axial failure.

[Paper 072]

A Parametric Study of R.C. Slab in Beam-Column Connection under Cyclic Loading

Saddam M. Ahmed, Umarani  Gunasekaran & Gregory A. MacRae

The slab effect on the beam flexural strength at the beam ends in buildings subjected to lateral loading, such as earthquake, is not fully understood and therefore it is not explicitly addressed in some of the design codes. As a result, designers often ignore the contribution of floor slabs to the lateral load resistance, or include it in a very approximate way. A simple and rational model to assess the slab contribution to beam strength for analysis and design has recently been developed for analysis and design. The model considers the effect of beam growth, bending effects and also the slab effect.

General expressions developed for the strength and stiffness contributions of the slab element depend on the reinforcement spacing, yield strength, and area, as well as the span length. In the present paper, the experimental results of four identical half-scaled beam-column joints are described. One is without a slab and remaining three have slabs of varied thickness and area of reinforcement. The slab-beam-column joints were tested under static displacement controlled cyclic loading and the experimental results are compared with the analytical results. It was found that the model is capable of capturing the key aspects of the experimental inelastic response of the beam-column connections very well.

[Paper 058]

Shake table tests of non-ductile RC frames retrofitted with GFRP laminates in beam column joints and selective weakening in floor slabs

P.Quintana  Gallo, U. Akguzel, S. Pampanin, A.J. Carr & P. Bonelli

As part of extensive experimental work done in the context of the project 'Retrofit Solutions for New Zealand Multi-Storey Buildings', a non-ductile RC frame model structure was tested on the shake table of the University of Canterbury. The 2/5 scale model was designed according to New Zealand's pre-1970's practice, comprising of two frames, one external, one internal, connected by means of transverse beams and floor slabs. The tests of the as-built specimen revealed a brittle inelastic mechanism with severe damage in first floor exterior beam column joints, under a specific ground motion.

In a following stage, Glass-Fibre Reinforced Polymer (GFRP) layers were implemented in beam column joints in order to strengthen and confine specific zones. Slabs were weakened in a configuration that reduces the negative flexural capacity of the longitudinal beam outside the GFRP, neutralizes transverse beam torsion effects, and allows for anchorage of GFRP layers. The retrofitted specimen tested under the same ground motions used for the as-built specimen, developed ductile flexural rotations in beams and bottom columns, proving the ability of this particular retrofit configuration of relocating brittle shear damage in exterior joints. In this paper the final retrofit intervention implemented and preliminary tests results are presented.

[Paper 116]

Experiments on Reinforced Concrete Frames with Brick Infill

Tsung-Chih  Chiou, Shyh-Jiann  Hwang & Fu-Pei  Hsiao

Brick walls constrained by a reinforced concrete (RC) frame on all four sides are quite often used in low-rise RC buildings. According to earthquake reconnaissance, a brick infilled wall is one of the major resistances of preventing building collapse. Therefore, understanding the seismic behavior of a brick infilled wall is essential in evaluating the seismic resistance of existing low-rise RC buildings. This research is aimed at examining the seismic behavior of brick infilled walls. Four full-scale RC frames with 200mm thickness brick walls were tested under cyclic loading. The main variables were the brick infilled walls with and without an inner-tied column, and the compression strength of mortar. The testing results indicated that the boundary columns and the inner-tied column of RC frame with brick infill were in shear failure. As well as, the ultimate lateral strength of brick infilled walls with an inner-tied column was 1.7 times of that of brick infilled wall without an inner-tied column. The increased compression strength of mortar was also beneficial to the seismic behavior of brick infilled walls. Test results showed that the RC frame could still have a mild negative slope of strength degradation for its post-strength behavior.

[Paper 085]

European research on seismic behaviour of precast structures

G. Toniolo

During the last two decades an extensive experimental and theoretical research activity has been carried out at European scale with the aim to investigate the seismic behaviour of precast structures. The attention has been addressed to frame systems for one-storey industrial buildings and multi-storey low-rise commercial buildings that have a very large diffusion in most European countries. The research campaigns accompanied the drafting and the publication of Eurocode 8 on Design of structures for earthquake resistance, leading to an organic set of specific principles and rules. Presently the research is still going on, again with a "co-normative" aim for next up-dating and revision of the same Eurocode.

The paper goes through this activity, describing the most important tests performed on full scale prototypes in the laboratories of Lisbon, Milan, Ljubljana, Athens, Istanbul and in the Joint Research Centre of the European Commission of Ispra. The results obtained are presented showing the state of the art and the innovative contributions that give to precast construction full reliability also in seismic regions.

[Paper 128]