Structural Concrete, Vol. 11, no. 4, December 2010

Written on 19 August 2011.

Flowable high-strength system as repair material

E. T. Dawood, School of Housing, Building and Planning, Universiti Sains Malaysia, Penang, Malaysia
M. Ramli, School of Housing, Building and Planning, Universiti Sains Malaysia, Penang, Malaysia 

The use of steel fibres in concrete or mortar is known for its potential to enhance the flexural toughness, the energy dissipation and the impact resistance for many structural applications, especially in building repairs and other civil engineering works. The use of steel fibres in flowable mortar provides a great advantage in arresting cracks and enhancing the flexural rigidity of the composite material. Hence, this experimental investigation was performed to provide a clear indication and understanding of the behaviour and structural performance in engineering construction. The experimental tests conducted were: density, compressive strength, splitting tensile strength, flexural strength and toughness indices tests. These tests are required to show that the best performance of high-strength flowable mortar or high-strength flowing concrete could be fulfilled by using steel fibres and the optimal percentages of silica fume as partial replacement of cement. The conductivity of the repair material was evaluated by adoption of some combined systems of repair materials with concrete to determine the bond action of this repair material (flowable high-strength system). The results indicate that the high-strength flowing concrete has an excellent performance in terms of compressive strength for the repaired system. On the other hand, the high-strength flowable mortar improves significantly the tensile strength of the repaired system. 

Structural Concrete, Vol. 11, no. 4, December 2010

Written on 19 August 2011.

Punching of RC slabs under eccentric loads

M. Farzam, University of Tabriz, Iran
N. A. Fouad, Institut für Bauphysik, Leibniz University,Germany
J. Grünberg, Institut für Bauphysik, Leibniz University,Germany
M. Y. Fard, University of Tabriz, Iran

The main objective of this paper is to study the effect of eccentricity of loads on the ultimate punching resistance and rotational capacity of slabs. A mechanical model recently proposed by Muttoni, which has been developed to predict the punching capacity of slab-column connections under concentric loads, is developed in the same manner as that of Broms to be applicable for the investigation of rotational capacity of slabs under eccentric loads. Furthermore, the effect of eccentricity of load on the ultimate punching resistance and the rotational capacity of slabs with respect to column is numerically studied performing a non-linear finite-element analysis using Atena. The numerical analyses consist of calculations of selected punching tests. The factors affecting the behaviour of the connections, such as the ratio of tension reinforcement, the type of reinforcement steel and the concrete compression strength are studied parametrically. The results of the analyses are compared with Eurocode 2 and ACI code predictions and with the mechanical model previously proposed by Broms and the model developed by Muttoni. 

Structural Concrete, Vol. 11, no. 3, September 2010

Written on 19 August 2011.

Study of underwater concrete using two-stage (preplaced aggregate) concrete in Libya

Hakim Abdelgader, Al-Fateh University, Libya
Manal Najjar, Al-Fateh University, Libya
Tareq Azabi, Bonyan Consulting Engineers, Tripoli, Libya 

Placement of concrete underwater is necessary in the implementation of most in-shore, and off-shore structures. The pouring of underwater concrete is considered to be a challenge for engineers, even during the design stage or during implementation and supervision. This is because many precautions must be taken to ensure the success of the casting process. The most important of these is to protect the fresh concrete from the water during the casting process to avoid the risk of wash-out of the cement past and segregation of aggregates. Concrete can be placed underwater successfully through good design of the concrete mix and choosing the most suitable method for placing of the concrete. There are new techniques for underwater concreting such as grouted aggregate; this is known as the two-stage concrete method. The main objective of this paper is to present the capability of pouring concrete underwater using this method. A laboratory model was prepared, visually investigated and tested by extracting core samples, then performing compressive, tensile and ultrasonic pulse velocity tests. From the results obtained it has been observed that concrete can be poured successfully underwater using the two-stage method, and it is recommended that this research may be developed by using different water-cement ratios and cement-sand ratios to obtain the optimum mix design; also, different types of aggregates, which are available in local quarries, may be used. 

Structural Concrete, Vol. 11, no. 4, December 2010

Written on 19 August 2011.

Torsion strengthening of RC beams with carbon fibre composites

J. J. Holtz Silva Filho, PUC-Rio, Brazil
E. de Souza Sánchez Filho, Fluminense Federal University, Brazil
M. de Souza Lima Velasco, PUC-Rio, Brazil

This paper presents the results of an experimental and theoretical study designed to evaluate the behaviour of reinforced concrete beams subjected to torsion and strengthened with carbon fibre composites. A total of seven beams, each with the dimensions 200x400x4200 mm, were tested. Test results reveal marked increases in the torsion capacity of 38% and 40% for each series of beams. The effective axial stress of a theoretical model for bonding the carbon fibre composites is incorporated in the space truss with softening model. The predictions of this proposed model are then compared with tests results. A high degree of agreement is verified between the experimental and theoretical values. 

Structural Concrete, Vol. 11, no. 3, September 2010

Written on 19 August 2011.

Deformations at flexural yielding of members with continuous or lap-spliced bars

Dionysis Biskinis, University of Patras, Greece 
Michael N. Fardis, University of Patras, Greece 

Models are developed and calibrated for the moment, the chord rotation and the secant stiffness at flexural yielding of reinforced concrete beams, rectangular columns or walls and members of T-, H-, U- or hollow rectangular section, on the basis of a databank of tests on members with continuous bars. Criteria are developed for the identification of adverse shear effects on the yield moment. The models apply only to members whose yield moment is not reduced by shear effects. They employ simple, explicit expressions suitable for practical application without moment-curvature analysis. They are extended to members with bars lap-spliced starting at the end section. The effect of biaxial loading on member yielding is examined. Most of the models have been adopted in Eurocode 8, Part 3. 

Structural Concrete, Vol. 11, no. 3, September 2010

Written on 19 August 2011.

Experimental investigations of partially-damaged RC beams and columns

Andrew Pullen, Imperial College London, UK 
Ali Abbas, Imperial College London, UK 

This paper summarises experimental investigations of undamaged and partially damaged reinforced-concrete beams and columns. The aim of the work was to establish and carry out experimental methods for determining the load-deformation behaviour and strength of these simple structural elements under varying levels of localised pre-damage (such as weakening or partial loss of concrete material). In particular, the effect of such partial/local damage on the overall behaviour and, crucially, its contribution to structural collapse, were also studied. There is little experimental evidence to validate predictions obtained from analysis or numerical modelling of partially damaged concrete members. Often, the ultimate capacity is the primary output of interest and it is usually determined using specimens that have no prior local damage. The present study produced data that led to a comparative study between the structural behaviour of both damaged and undamaged structural elements in order to help understand the effect of local damage and its contribution to structural collapse. The experimental results can also be used for future modelling and validation purposes.