N.C. Das Gupta

Coconut fibre reinforced corrugated slabs

Abstract This investigation reports a feasibility study of making coconut fibre reinforced corrugated slabs for use in low cost housing particularly for developing countries. The casting technique for production of corrugated slabs is discussed. Flexural tests have been carried out on corrugated slabs to determine their strength with different volume fractions and aspect ratios of fibres. Tests to determine the thermal and acoustic properties of these slabs are also reported. The experimental results are presented and discussed.

Natural geosynthetic drain for soil improvement

Abstract A geosynthetic vertical drain known as Fibredrain was developed using organic fibres from jute and coir to improve thick soft clay deposits. In addition, it was required to withstand the application of high energy impact on surface fills implemented as a part of soil improvement works. Some laboratory tests conducted to examine the relevant properties of this drain under simulated field conditions are presented. The drain was used in several construction projects in the southeast Asian region involving reclamation fills overlying marine clay, dynamic replacement and mixing (DRM) method of treating peaty soils underlain by fluvial clays and housing projects built on mine tailings. The back analysis of field behaviour of the drain shows that it has adequate discharge capacity for consolidation of highly plastic clays; its effectiveness lasts for observed periods of over 2 years and its function as a vertical drain is unimpaired when used in conjunction with high energy impact application. The relatively low cost of manufacture using indigenous material and local labour makes this drain attractive in countries where jute and coir are abundant as well as where ecological considerations are important as this drain is biodegrable.

OPTIMIZATION OF PRESTRESSED CONCRETE BRIDGE GIRDERS

This paper presents an application of generalized geometric programming to the optimal design of a prestressed concrete box bridge girder. The actual cost of construction consisting of prestressing. formwork and concrete is minimized. Constraints are formulated as stipulated by the British Code of Practice CP110. The constraints of the geometric program relate to bending and shear stresses, and geometric criteria. A sample design is presented and sensitivity studies are performed to test the influence of major design parameters on cost factors.

Design of reinforced concrete cylindrical water tanks for minimum material cost

Abstract The minimum material cost design of reinforced concrete cylindrical water tanks according to BS8007 is considered. The material cost takes into account the amount of reinforcement and concrete required. The analysis is simplified by using the beam on elastic foundation (BEF) analogy. The tank wall is modelled as consisting of linear piecewise slopes. The non-linear constrained minimization problems have been solved numerically by direct search methods using a microcomputer. The results are presented and discussed.

Minimum weight design of multi-bay multi-storey steel frames

Abstract The present paper considers the minimum weight (volume) design of multi-bay multi-storey steel frames according to BS5950. The problems are formulated as nonlinear constrained minimization problems and then solved using numerical optimization techniques. The study illustrates different possible configurations of sections based on minimum weight designs. The problems have been solved using a 80386-25 microcomputer equipped with a math co-processor.

An application of geometric programming to structural design

Abstract This paper presents an application of generalised geometric programming to an optimal design of a modular floor system, which consists of reinforced solid concrete and voided slab units supported on steel beams. A function representing the cost of the floor system in terms of design variables, length, width and thickness of components, and other engineering and cost parameters is minimized subject to various constraints depending on stresses and deflections. A dual-based algorithm has been used for solving the design problem. Analyses are performed to determine the changes in the optimal values of the design variables with respect to the changes in imposed loads on the floor system.

A GEOMETRIC PROGRAMMING METHOD FOR COST-OPTIMAL DESIGN OF A MODULAR FLOOR SYSTEM

Geometric programming has been found suitable for optimal design of many engineering systems. This paper presents a method based on geometric programming for cost-optimal design of a modular floor system with precast prestressed slab units simply supported on steel beams. Both voided and solid slab constructions are considered. The objective function of the optimization problem includes cost of fabrication incuding concrete, formwork, prestressing and steel beams and cost of erecting the structure. The constraints are formulated based on allowable stresses, deflections and geometry of the structural systems. The optimization problem is solved to obtain the optimal values of the design variables. Sensitivity analyses are then performed to determine the effect of changes in the imposed load on the optimum values of the design variables.

Controlled tropical curing method for accelerated concrete strengths

Abstract Accelerated curing and testing of concrete can be used for both quality control and quality assurance. This paper presents controlled curing and accelerated curing methods for early assessment and prediction of strength of concrete and discusses their relative merits. The controlled curing method utilises the inherent high ambient temperature of the tropics without the artificial heating needed for other accelerated curing methods. The test specimens are controlled cured for only 24 hours prior to testing. A series of compressive strength tests were conducted on concrete of varying proportions. Two types of water reducing admixtures were used individually in some mixes. A multiple linear regression technique has been adopted where appropriate to correlate the 28-day standard cured strength with the controlled cured strength, 35° cured strength, 55° cured strength and standard 2 day and 3 day strengths. The correlation results are discussed in detail. The important observations arising in this study are: the simplicity of the controlled curing method; the reliability of multiple linear regression relations; and the small effect of admixtures on the correlations between strengths.

Optimal Design of Prestressed Concrete Composite Slab by Geometric Programming

Geometric programming (GP) has been found suitable for optimal design of many engineering systems. This paper presents a method based on GP for cost-optimal design of prestressed concrete panel composite slab. Precast prestressed concrete panels are used as formwork for .cast-in-situ reinforced concrete floor slab. The objective function of the optimization problem includes cost of concrete, prestressing, erection and reinforcing. The constraints are formulated based on allowable stresses, deflections and geometry of the structural systems. The optimization problem is solved to obtain the optimal values of the design variables.

Optimal Bridge Design by Geometric Programming

This paper presents an application of generalized geometric programming to the optimal design of a prestressed concrete pedestrian bridge deck. The actual cost of construction consisting of prestressing, formwork and concreting is minimized. Constraints are formulated as stipulated by the British Code of Practice CP 110, related to bending and shear stresses and minimum concrete cover. A sample optimal design is included in the paper. The method presented can be applied to other engineering design problems by appropriately modifying the problem formulation.