Repair and rehabilitation of concrete structures using confinement: A review

Four groups of axial compression tests on hexagonal CFT stub columns have been carried out aiming to investigate the effects of the concrete strength and steel ratio on the behaviour of hexagonal CFT stub columns. Studies on parametric analysis and composite action between core concrete and steel tube have been carried out using FE modelling which had been benchmarked using the test data. Based on the essential data obtained in this paper, the ratio of axial stress-yield strength of steel tube was determined at the ultimate state. The stress contour of core concrete was simplified to an unconfined area without constraint and a confined area with uniform constraint imposed by hexagonal steel tube. Eventually, a practical design equation of the ultimate bearing capacity of hexagonal CFT stub columns was proposed based on the superposition principle. An excellent agreement between the proposed equation and the experimental results was observed, with an average ratio of predicted to measured capacity of 1.08 and a standard deviation of 0.05.

Composite action of octagonal concrete-filled steel tubular stub columns under axial loading

In this paper, thirty-six short columns with different diameters (150 mm ≤ d ≤ 460 mm) and steel ratios (4.0% ≤ α ≤ 10.0%) were tested to failure to investigate the size effect of circular concrete-filled steel tubular short columns subjected to axial compression. Size effects on the peak axial stress, peak axial strain, composite elastic modulus, and ductility coefficient were studied. The experimental results showed that the peak axial stress, peak axial strain and ductility coefficient of the specimens tended to decrease with the increase in the column diameter. The values of the composite elastic modulus remained almost constant when the diameter of the specimens increased, indicating that size effect on the composite elastic modulus was not obvious. Meanwhile, size effect on the peak axial stress was influenced by the steel ratio in the range of 4–10%. Furthermore, the size effect tended to decrease as the steel ratio increased. By comparing with the current codes, a reduction coefficient was introduced to consider the size effect of concrete core. Based on the reduction coefficient, the size effect of the concrete core inside the steel tube is found to be weaker compared with that of the unconfined concrete columns because of the confinement effect.

Size effect of circular concrete-filled steel tubular short columns subjected to axial compression

Concrete filled steel tubes (CFSTs) show advantageous applications in the field of construction, especially for a high axial load capacity. The challenge in using such structure lies in the selection of many parameters constituting CFST, which necessitates defining complex relationships between the components and the corresponding properties. The axial capacity (Pu) of CFST is among the most important mechanical properties. In this study, the possibility of using a feedforward neural network (FNN) to predict Pu was investigated. Furthermore, an evolutionary optimization algorithm, namely invasive weed optimization (IWO), was used for tuning and optimizing the FNN weights and biases to construct a hybrid FNN–IWO model and improve its prediction performance. The results showed that the FNN–IWO algorithm is an excellent predictor of Pu, with a value of R2 of up to 0.979. The advantage of FNN–IWO was also pointed out with the gains in accuracy of 47.9%, 49.2%, and 6.5% for root mean square error (RMSE), mean absolute error (MAE), and R2, respectively, compared with simulation using the single FNN. Finally, the performance in predicting the Pu in the function of structural parameters such as depth/width ratio, thickness of steel tube, yield stress of steel, concrete compressive strength, and slenderness ratio was investigated and discussed.

https://www.mdpi.com/1996-1944/13/5/1205/pdf

Optimization of Artificial Intelligence System by Evolutionary Algorithm for Prediction of Axial Capacity of Rectangular Concrete Filled Steel Tubes under Compression.

This work aims to develop a novel and practical equation for predicting the axial load of rectangular concrete-filled steel tubular (CFST) columns based on soft computing techniques. More precisely, a dataset containing 880 experimental tests was first collected from the available literature for the development of an artificial neural network (ANN) model. An optimization strategy was conducted to obtain a final set of ANN’s architecture as well as its weight and bias parameters. The performance of the developed ANN was then compared to current codes (AS, EN, AIJ, ACI, AISC, LRFD, and DBJ) and existing empirical equations. The accuracy of the present model was found superior to the results obtained by others when predicting the axial load of rectangular CFST columns. For practical application, an explicit equation and an Excel-based Graphical User Interface were derived based on the ANN model. The graphical user interface is provided freely for all interested users, to support the design, teaching, and interpretation of the axial behavior of CFST columns.

Prediction of axial load capacity of rectangular concrete-filled steel tube columns using machine learning techniques

In this study, compressive strength, modulus of elasticity and steel tensile coupon tests are performed to determine material properties. Sixteen hollow cold formed steel tubes and 48 concrete filled steel tube specimens are used for axial compression tests. The effects of width/thickness ratio (b/t), the compressive strength of concrete and geometrical shape of cross section parameters on ultimate loads, axial stress, ductility and buckling behavior are investigated. Circular, hexagonal, rectangular and square sections, 18.75, 30.00, 50.00, 100.00 b/t ratio values and 13, 26, 35 MPa concrete compressive strength values are chosen for the experimental procedure. Analytical models of specimens are developed using a finite element program (ABAQUS) and the results are compared. Circular specimens are the most effective samples according to both axial stress and ductility values. The concrete in tubes has experienced considerable amount of deformations which is not expected from such a brittle material in certain cases. The results provide an innovative perspective on using cold formed steel and concrete together as a composite material.

Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

Two series of tests were conducted to investigate the behavior of local thin jacketing for the retrofitting of reinforced concrete (RC) columns. In the first series, four full-scale RC columns with a height of 400 cm and a 30 cm square cross-section were tested under constant axial load and reversed cyclic lateral displacements. The heavily damaged columns were retrofitted with local thin jacketing. Self-compacting concrete (SCC) was used in the production of 7.5 cm thick, four-sided jacketing. The height of the jacketing was 100 cm for one specimen and 200 cm for all others. In the second series, the retrofitted columns were retested with the same axial load and displacement history. The effectiveness of local thin jacketing in the retrofitting of RC columns was examined with respect to lateral strength, stiffness, inelastic load-deformation behavior and energy dissipation.

Local thin jacketing for the retrofitting of reinforced concrete columns

Five to 10% of buildings in earthquake prone areas, with structural deficiencies and non-structural partitioning walls are expected to collapse totally during a severe earthquake. Relying on the encouraging early test results, transforming a selected number of non-structural partitioning walls to structural walls has been considered as one of the realistic preventive measures if sufficient reliability is achieved both experimentally and theoretically. The major part of the recent experimental and theoretical works of The Structural and Earthquake Engineering Laboratory of Istanbul Technical University (ITU) has been devoted to achieve better understanding of the seismic behavior of brittle partitioning walls which are generally ignored in the design, rehabilitation design or evaluation stages of ordinary low-cost, low-rise, reinforced concrete relatively old buildings. In this chapter the complementary tests and analytical works carried out for this purpose are summarized to come up with a cost-effective prescriptive solution to prevent the total collapse of buildings. The proposed retrofitting technique is exemplified through the mathematical models of strengthened buildings offered by codes which are reviewed as well. The experimentally developed data such as the modulus of elasticity of clay brick walls, damping ratios, shear strength of improved partitioning walls and earthquake load reduction factors are referred in the analyses.

Improved Infill Walls and Rehabilitation of Existing Low-Rise Buildings

This paper presents a review of the proposed design for assessing the tensile capacity of a simply truss framing system of cold-formed steel. A series of connection tests were made to investigate the capacity of connections by its deformation and load caring capacity. Furthermore, Screw connections were compared to adhesive connections. Those were created of 1 screw to 3 installed screw using 8 mm screw. On the other hand, 50%, 75% and 100% percentage of adhesive, i.e., A3M and ASK were also added to be evaluated. As a result, the experimental condition was carried out for developing a model to predict the performance capacity of each specimen. The test specimens are a single lap C connection with one end fixed by a grip, and the other end is tensioned. Each specimen was subjected to the load maximum capacity and the load deformation behaviour. The adhesive material was made of the total area of screw connection which is controlled by the volume of its area. Further, the comparison connection was considered for the analysis of the connection capacity, which was estimated from the specimen’s maximum load and the load-deformation behaviour. This research is also considered to face the problem of significant fracture mechanism and used as a further alternative solution. As a result, both adhesive materials could easily displace screw connection. ASK has a lower strength capacity than A3M but implied a better fracture mechanism. It was offered nearly similar behaviour and was suggested to evaluate the behaviour of screw-adhesive connection in advance.

/pdf/assessing-the-tensile-capacity-of-cold-formed-steel-46biqh73pe.pdf

Kivanc Taskin

Papers

Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

Local thin jacketing for the retrofitting of reinforced concrete columns

Improved Infill Walls and Rehabilitation of Existing Low-Rise Buildings

Assessing the Tensile Capacity of Cold-Formed Steel Connections using Self-Drilling Screws and Adhesive Materials

Automated topology design of high-rise diagrid buildings by genetic algorithm optimization