Muhammad N. S Hadi

Behaviour of externally confined high-strength concrete columns under eccentric loading

Previous studies proved that the application of FRP can eliminate some unwanted properties of high-strength concrete, such as the brittle behaviour of high-strength concrete. However, research studies conducted so far on external confinement of concrete columns have mainly concentrated on concentric loading. This paper experimentally investigates the performance of externally confined high-strength concrete columns subjected to eccentric loading and evaluates the effectiveness of two confinement materials-carbon fibre and E-glass. Plain columns were wrapped with either carbon fibre or E-glass with different number of layers. Two reference columns were internally reinforced and tested. The enhancement of the strength of the plain column specimens under eccentric loading is not so pronounced as for the concrete specimens under concentric loading, especially for the high strength concrete specimens. However, when wrapped, the columns achieved a considerable gain in strength compared to plain concrete columns.

Neural networks applications in concrete structures

This paper presents and discusses the applications of neural networks in concrete structures. It aims at introducing neural networks applications in structural design. The paper covers two applications of neural networks in concrete structures. Backpropagation networks are chosen for the proposed network, which is written using the programming package MAT-LAB. The overall results are compared and observed for the performance of the networks. Based on the applications it was found that neural networks are comparatively effective for a number of reasons, which include the amount of CPU memory consumed by neural networks is less than that consumed by conventional methods and their ease of use and implementation, neural networks provide both the users and the developers more flexibility to cope with different kinds of problems.

New Method of Strengthening Reinforced Concrete Square Columns by Circularizing and Wrapping with Fiber-Reinforced Polymer or Steel Straps

AbstractThis study investigates three methods of strengthening existing reinforced square concrete columns under different loading conditions. Four groups of sixteen reinforced concrete square columns were made from normal-strength concrete. Reinforcement was kept at minimum ratio, simulating columns that need retrofitting. Columns of the first group were reference columns (Group N), while the corners of the second group columns (Group RF) were rounded and wrapped with three layers of carbon-fiber-reinforced polymers (CFRPs). The sides of the columns of the third group (Group CF) were bonded with four pieces of concrete with a segmental circular shape, thus changing the cross section of the column from a square to a circle before each column was wrapped with three layers of CFRP. The columns of the last group (fourth) were modified as the third group to result in a circular cross section, but were confined with steel straps. Results from the study showed that all confinement methods increased the capacity...

Non-linear finite element analysis of flexible pavements

A research study is being undertaken to incorporate the realistic material properties of the pavement layers and the moving traffic load, in the analysis of flexible pavements, using the finite element theory. As a preliminary step taken herein in this direction, a pavement structure where field measurements have been carried out when subjected to a cyclic loading, is selected and modelled as a finite element model. The analysis is being carried out using the finite element computer package ABAQUS/STANDARD, when this pavement model is subjected to static and cyclic loading while considering the linear and non-linear material properties of the pavement layers. The results indicate that displacements under cyclic loading when non-linear materials are present, are the closest to field measured deflections.

Optimal direct (static) output feedback controller using real coded genetic algorithms

This paper considers a genetic based optimisation procedure for designing the control force in actively controlled structures. Two optimal output feedback controllers utilising H2 and H∞ optimal control are discussed in this paper where only a limited number of sensors is used. In addition, the feedback control used in this paper is a static (direct) output feedback control where the gain can be multiplied directly with the measurement output. Therefore, it is not necessary to construct an observer to estimate the state as in the case of dynamic or observer based controller. The optimisation to minimise the H2 and H∞ norms are solved using real coded genetic algorithms, which have the ability to explore the unknown domain of the solution. Numerical examples are then carried out to the structures utilising active tuned mass damper and active bracing systems to show the applicability of the proposed procedure.

Heuristic Approach for Optimum Cost and Layout Design of 3D Reinforced Concrete Frames

AbstractThis paper presents a new methodology for cost optimization of the preliminary layout design of three-dimensional (3D) reinforced concrete (RC) frames. This approach is capable of being easily employed for the optimal layout design of a realistic large RC structure that accounts for constraints imposed by design standards. The new approach considers modeling, structural analysis, concrete member design, and discrete optimization together with data on the cost of systems and materials. The methodology is comprised of two parts. First, using the cross-sectional action effects as design variables, a heuristic cost function is presented as an alternative to traditional cost functions for layout optimization of RC structures. Using the presented cost function, a structural optimization problem is formulated for column layout design of 3D RC frames. Then, an ant system algorithm, a discrete method, is proposed to solve the cost optimization problem. Two comparative design examples are included to demons...

Experimental Investigations on Circular Concrete Columns Reinforced with GFRP Bars and Helices under Different Loading Conditions

AbstractGlass-fiber-reinforced polymer (GFRP) bar has emerged as a preferable alternative to steel bar in reinforced concrete (RC) members in harsh, corrosive, coastal environments in order to eliminate corrosion problems. However, only limited experimental studies are available on the performance and behavior of concrete columns reinforced with GFRP bars under different loading conditions. This study investigates the use of GFRP bars and GFRP helices (spirals) as longitudinal and transversal reinforcement, respectively, in RC columns. A total of 12 circular concrete specimens with 205-mm diameter and 800-mm height were cast and tested under different loading conditions. The effect of replacing steel with GFRP reinforcement and changing the spacing of the GFRP helices on the behavior of the specimens was investigated. The experimental results show that the axial load and bending moment capacity of the GFRP-RC columns are smaller than those of the conventional steel-RC columns. However, the ductility of th...

Passive and active control of three‐dimensional buildings

The majority of the recent research effort on structural control considers two-dimensional plane structures. However, not all buildings can be modelled as plane structures, thus limiting the capability of the proposed procedures only to regular and symmetrical structures. A new procedure is developed in this paper to analyse three-dimensional buildings utilizing passive and active control devices. In the building model, the floors are assumed rigid in their own plane resulting in three degrees of freedom at each floor. Two types of active control devices utilizing an active tuned mass damper and an active bracing system are considered. The effect of passive mass dampers and active control force in the equations of motion is incorporated by using the Hamiltons principle. The passive parameters of the dampers as well as the controller gain is then optimized using a genetic based optimizer where the H 2 , H∞ and L 1 norms are taken as the objective functions.

Retrofitting of shear failed reinforced concrete beams

This paper considers the strength and load carrying capacity enhancement of reinforced concrete beams that have been tested and failed in shear. A total of sixteen sheared beam specimens with a length of 1.2 m and cross-sectional area of 100 by 150 mm were retrofitted by using various types of fibre reinforced polymer (FRP) and then retested. The retrofitted beam specimens wrapped with different amounts and types of FRP were subjected to four-point static loading. Load, deflection and strain data were collected during testing the beam specimens to failure. Results of the experimental program indicate that there are several parameters that affect the strength of the beams. The results also show that the use of FRP composites for shear strengthening provides significant static capacity increase.

Use of Helixes in Reinforced Concrete Beams

This paper considers the strength gain and ductility of high-strength reinforced concrete (HSRC) beams incorporating an increase in tensile reinforcement. The effect on ductility through the application of helical reinforcement located in the compressive region of the beam is also investigated. Beams of span 4 m were subjected to flexural loading, with emphasis placed on the midspan deflection. Results indicated that helical reinforcement is an effective way of increasing ductility in HSRC beams. If the correct pitch is utilized for effective confinement, helical reinforcement will provide an economical solution for enhancing the strength of flexural members.