ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 05 Feb 2023 11:22:22 GMT2023-02-05T11:22:22Z50251- COLLAPSE LOADS IN PURE TORSION OF REINFORCED CONCRETE BEAMS CONTAINING AN OPENING.https://scholarbank.nus.edu.sg/handle/10635/74104Title: COLLAPSE LOADS IN PURE TORSION OF REINFORCED CONCRETE BEAMS CONTAINING AN OPENING.
Authors: Mansur, M.A.; Alwis, W.A.M.
Abstract: A simple method is presented for calculating the ultimate strength of a reinforced concrete beam that contains a large rectangular opening and is subjected to pure torque. A comparison of the theoretical predictions with the available test data shows good agreement. The method is used to define small and large openings.
Sun, 01 Jan 1984 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/741041984-01-01T00:00:00Z
- Elastoplastic analysis of skeletal structures by plastic strain methodhttps://scholarbank.nus.edu.sg/handle/10635/74156Title: Elastoplastic analysis of skeletal structures by plastic strain method
Authors: Alwis, W.A.M.
Abstract: A method for first-order analysis of nonholonomic elastoplastic skeletal structures is presented. The governing equations are formed by expressing the elastic and the residual stresses as linear functions of the applied loads and the plastic strains, respectively. The yield surface is linearized and the yield constraints and the flow rule are introduced as auxiliary conditions. The load-deformation behaviour is traced along a sequence of phases, each of which is governed by linear equations and terminated by a plastic event. An interactive numerical procedure that implements this method is also presented. A specific feature of the approach is its ability to provided the complete solution whenever nonunique kinematic solutions arise.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/741561991-01-01T00:00:00Z
- Response spectrum of underground protective structureshttps://scholarbank.nus.edu.sg/handle/10635/50729Title: Response spectrum of underground protective structures
Authors: Alwis, W.A.M.; Lam, K.Y.
Abstract: The rigid-body response of underground protective structure is analyzed adopting a single-degree-of-freedom model. A recently proposed decoupling procedure is used to accomodate the structure-medium interaction. A response spectrum that describes the internal shock environment is derived as a simple closed form expression. This spectrum can be used for preliminary design and cost optimization studies. © 1994.
Thu, 01 Dec 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/507291994-12-01T00:00:00Z
- Computer-aided dam break flow routinghttps://scholarbank.nus.edu.sg/handle/10635/50681Title: Computer-aided dam break flow routing
Authors: Liong, S.Y.; Tan, C.C.; Alwis, W.A.M.; Selvalingam, S.
Abstract: A computer aided dam-break flow routing program, CADAMBRK, has been developed on the Integraph system. CADAMBRK is based on the widely used dam break analysis program, DAMBRK. However, unlike DAMBRK which uses the rigidly formatted text data file. CADAMBRK operates in a user friendly environment and possesses three additional special features, namely: (1) a digital terrain model, (2) a markedly enhanced graphical plot capability for hydrograph and flood zone identification, and (3) suggested values for overland flow roughnesses to be used in the dam-break generated flood routing. The paper discusses the structure of the program, the various representative modules, and presents results of a hypothetical dam break generated flood. © 1991.
Wed, 01 May 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/506811991-05-01T00:00:00Z
- Nonholonomic analysis of elastoplastic frameshttps://scholarbank.nus.edu.sg/handle/10635/65874Title: Nonholonomic analysis of elastoplastic frames
Authors: Alwis, W.A.M.
Abstract: A procedure for progressive nonholonomic analysis of elastoplastic plane frames neglecting axial force effects is developed. Within the framework of simple plastic theory the governing condition is expressed in terms of total values of loads, bending moments, and hinge rotations. The path-dependent load-deformation behaviour is traced incrementally through linear phases, imposing the yield criterion and flow rule as auxiliary conditions. The method is intended for implementation as an interactive system for analysis and design. Computations are organized as a series of four modules such that a loading data modification can be responded to with little effort and the next fastest response is for changes in member sections, nodal coordinates, and structural connectivity, in that order. Deflection components are computed only as and when queried by the user. A special feature of the approach is that the complete solution can be provided whenever lack of uniqueness of kinematic solution arises. A detailed example is included.
Sun, 01 Dec 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/658741991-12-01T00:00:00Z
- Reinforced fibre concrete deep beams with web openingshttps://scholarbank.nus.edu.sg/handle/10635/66064Title: Reinforced fibre concrete deep beams with web openings
Authors: Mansur, M.A.; Alwis, W.A.M.
Abstract: Test results of 12 reinforced fibre concrete deep beams with rectangular openings in the web are reported. The beam dimensions and the size of openings were kept constant. The major parameters of the study were the volume fraction of fibres, opening location, shear span to effective depth ratio and the amount of web reinforcement. Test results indicate that the amount of web reinforcement, either in the form of discrete fibres or as continuous reinforcement, and the location of opening are the principal parameters that affect the behaviour and strength of deep beams. Available strength equations for non-fibre concrete deep beams are shown to provide a reasonable prediction of the ultimate strength for fibre concrete as well. © 1984.
Thu, 01 Nov 1984 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/660641984-11-01T00:00:00Z
- Kinematic nonuniqueness of elastoplastic structureshttps://scholarbank.nus.edu.sg/handle/10635/65740Title: Kinematic nonuniqueness of elastoplastic structures
Authors: Alwis, W.A.M.
Abstract: Lack of uniqueness of the kinematic solution of structures, analyzed as an assemblage of discretized elements assuming nonholonomic linearly-elastic/perfectly-plastic behaviour and a linearized yield surface, is studied. The occurrence of an elastoplastic mechanism leads to nonuniqueness; an elastoplastic mechanism is defined as a kinematically-admissible strain rate field made up of an admissible elastoplastic solution of the governing conditions and an add-on variable component consisting of a linear combination of plastic (collapse) mechanisms. The scalar multipliers of this linear combination are bounded, except at plastic collapse in which case the elastoplastic mechanism degenerates to a plastic mechanism. In the space of loads, the load paths that could coexist with nonuniqueness are restricted to a hyperplane or a crease of intersection of hyperplanes, defined by the equilibrium equations arising from the associated plastic mechanisms of the elastoplastic mechanism. The difference between any two competing displacement vectors would be normal to that hyperplane or crease, in the same manner plastic strain rates are to the yield surface according to the flow rule. © 1991.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/657401991-01-01T00:00:00Z
- Long-term deflection of RC beamshttps://scholarbank.nus.edu.sg/handle/10635/65778Title: Long-term deflection of RC beams
Authors: Alwis, W.A.M.; Olorunniwo, A.; Ang, K.K.
Abstract: Long-term deflection of statically determinate reinforced concrete beams under service loads is analytically studied. The BP-2 creep and shrinkage model is adopted and extended to accommodate concrete tensile behavior by assuming a tensile stress-strain relation. The creep rate is related to the stress in the same manner for both tension and compression. Beam deflection is determined using curvatures computed by assuming that the total strain varies linearly across depth (Bernoulli-Navier hypothesis). Available test results for 37 beams are compared with deflection predictions by this numerical scheme and by applications of the same model after simplification using effective modulus methods. Further comparisons are made with the 1983 ACI Building Code method and a recent method proposed by Bazant and Oh. The direct implementation of the extended BP-2 model is observed to be the most accurate. The results demonstrate that a realistic model of creep strains can lead to good estimates of deflection. Furthermore, the results indicate that the contribution of shrinkage to overall deformation can be significant.
Fri, 01 Jul 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/657781994-07-01T00:00:00Z
- Long-term deflection of RC beams under constant loadshttps://scholarbank.nus.edu.sg/handle/10635/65779Title: Long-term deflection of RC beams under constant loads
Authors: Alwis, W.A.M.
Abstract: A method of constructing a time-dependent bilinear moment-curvature curve for reinforced concrete beams is proposed and its use for estimating long-term deflection of statically determinate beams under constant loading is demonstrated. The moment-curvature relationship defined herein is meant for a beam length subjected to a constant moment profile as opposed to a section subjected to a varying moment. The time-dependent concrete material behaviour subjected to the environmental humidity and temperature conditions is assumed to be characterised by the shrinkage strain and an effective modulus. The beam behaviour is then derived by considering uncracked and fully cracked sections. A linearised moment-curvature relationship is adopted in the post-cracking range, for taking into account the tension stiffening effect. Deflections of four example test beams are calculated, adopting an available concrete model to determine the shrinkage strain and effective modulus using concrete mix proportions and other beam data together with assigned constant values of humidity and temperature for the test duration. Comparison with measured deflections show that a reasonable level of accuracy can be achieved by the proposed approach. © 1998 Elsevier Science Ltd. All rights reserved.
Mon, 01 Feb 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/657791999-02-01T00:00:00Z
- Limit analysis using systematically generated mechanismshttps://scholarbank.nus.edu.sg/handle/10635/65763Title: Limit analysis using systematically generated mechanisms
Authors: Alwis, W.A.M.
Abstract: A simple and efficient computer method for limit analysis of structures that obey the 'square' yield criterion is presented. A new method of generating mechanisms is developed and employed to systematically arrive at the collapse solution by operating on a compact solving system. The entire algorithm is explained using the principles of limit analysis, by establishing the physical meaning of expressions derived. The method is suitable for implementation in micro-computers and for use as a teaching tool. Examples are provided to clarify the theoretical aspects and application. © 1988.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/657631988-01-01T00:00:00Z
- Nonuniqueness in elastoplastic frameshttps://scholarbank.nus.edu.sg/handle/10635/65887Title: Nonuniqueness in elastoplastic frames
Authors: Alwis, W.A.M.
Abstract: Lack of uniqueness of the kinematic solution of elastoplastic flexural frames is studied by deriving a general solution for nonholonomic behavior. A singular hinge set is defined as a collection of plastic hinges that would form a mechanism if they were replaced by mechanical hinges. It is shown that whenever singular subsets can be found among active plastic hinges, the kinematic solution may become nonunique. The rate of work done by the load rates on the contributing mechanisms must be zero if a prevailing nonuniqueness is to sustain.
Tue, 01 Sep 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/658871992-09-01T00:00:00Z
- Dynamic response of elasto-plastic planar archeshttps://scholarbank.nus.edu.sg/handle/10635/65460Title: Dynamic response of elasto-plastic planar arches
Authors: Lee, S.L.; Swaddiwudhipong, S.; Alwis, W.A.M.
Abstract: The behaviour of elasto-plastic planar arches subjected to dynamic loads in presented. The governing equations are formulated through the dynamic equations and compatibility conditions The latter is established by applying the generalized conjugate segment analogy. Bending moments at the nodes and axial forces in the members are considered as primary variables in the elastic regime. They are supplemented by the rotations at the nodes and dislocations in the elements when plastic hinges occur. Newmark-β method is adopted in the time marching process. The interaction diagram of each element is treated as the yield surface for the element and the associated flow rule is enforced as plastic flow occurs. The method provides good prediction of dynamic response of elasto-plastic arches while requiring small core storage and short computer time.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654601996-01-01T00:00:00Z
- Discrete element slip model of plasticityhttps://scholarbank.nus.edu.sg/handle/10635/65436Title: Discrete element slip model of plasticity
Authors: Alwis, W.A.M.
Abstract: A two-dimensional domain under plane-stress conditions is considered. The admitted external loading comprises a unidirectional uniform body force and distributed forces along the boundary. By considering a discrete element slip model and applying the principle of virtual work, a comprehensive set of equilibrium equations purely in terms of the average shear stress along edges of a triangulated mesh in derived. Plastic collapse by incompressible flow due to shear failure at a limit stress can thereby be analyzed. The collapse mechanisms therein would contain tangentially discontinuous velocity fields. The coefficient of each shear stress term in the equilibrium equations is the sum of cotangents of two vertex angles in the mesh, whereas the coefficient of each boundary normal stress term is plus or minus unity. The number of internal nodes, boundary nodes and restrained boundary edges, together with the degree of connectivity of the domain, are adopted as primary quantifiers of the size of the numerical problem. © 2000 Elsevier Science Ltd.
Wed, 01 Nov 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654362000-11-01T00:00:00Z
- Elasto-plastic dynamic analysis of plane frames and deep archeshttps://scholarbank.nus.edu.sg/handle/10635/65524Title: Elasto-plastic dynamic analysis of plane frames and deep arches
Authors: Lee, S.L.; Alwis, W.A.M.; Swaddiwudhipong, S.; Mairantz, B.
Abstract: The dynamic response of elasto-plastic frames and arches is investigated using a discrete system approach. The governing equations of motion are formulated through the virtual work principle and supplemented by the compatibility conditions established through the conjugate segment analogy. Time marching is carried out through direct time integration process using backward differences. The method, requiring small core storage and short computer time, can be easily implemented on any personal computer. © 1988 Springer-Verlag.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/655241988-01-01T00:00:00Z
- Axisymmetric Plastic Plates with Ring Supports at Optimum Locationshttps://scholarbank.nus.edu.sg/handle/10635/65195Title: Axisymmetric Plastic Plates with Ring Supports at Optimum Locations
Authors: Wang, C.M.; Ting, S.K.; Alwis, W.A.M.
Abstract: This study examines plastically designed axisymmetric Tresca plates of uniform thickness supported on multiple internal concentric rings. The plate is assumed to be under uniformly distributed load. The optimization problem of maximizing the load-carrying capacity of the plate by suitable positioning of a given number of supports is considered. The improvement of the carrying capacity that could be achieved by such an optimization is significant, as shown by the results obtained herein. These optimal solutions should be useful to designers for measuring the efficiency of their designs and also provide clues as to which segments of the internally supported plate are liable to collapse.
Tue, 01 Feb 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/651951994-02-01T00:00:00Z
- Buckling of tapered circular plates: Allowances for effects of shear and radial deformationhttps://scholarbank.nus.edu.sg/handle/10635/65271Title: Buckling of tapered circular plates: Allowances for effects of shear and radial deformation
Authors: Wang, C.M.; Tan, T.J.; Hong, G.M.; Alwis, W.A.M.
Abstract: Elastic axisymmetric buckling of tapered circular plates under a compressive radial load is analyzed. The effects of shear and prebuckling radial deformation are considered in the analysis because they are important when plates are thick. No previous buckling data are known to exist for tapered circular plates with allowance for both of these effects. The buckling analysis is performed using the Rayleigh-Ritz method. The shooting method is used in the computation of the varying stress function along the plate radius. Comprehensive generic buckling results for circular plates with linearly or parabolically varying thickness are presented. It is noted that shear deformation tends to reduce the buckling load. However, this reduction in buckling load is somewhat offset by the strength-enhancing effect of prebuckling radial deformation that is smaller but of the same order of magnitude. Optimal taper parameter values for such tapered plates are obtained. It is found that the optimal taper is insensitive to the effects of shear and prebuckling radial deformation. In general, these effects on the buckling load are more significant for plates with optimal tapers.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/652711996-01-01T00:00:00Z
- Computer aided optimal plastic designhttps://scholarbank.nus.edu.sg/handle/10635/65332Title: Computer aided optimal plastic design
Authors: Alwis, W.A.M.
Abstract: An interactive method for optimal plastic design of structures that obey the square yield criterion is presented. Sections of fixed dimensions such as standard sections can be used for design and realistic cost estimates can be used in assessment. The design is developed interactively by upgrading in steps, using the rate of increase of strength per unit incremental cost as a guide. The entire method is explained by establishing the physical meaning of the expressions derived. The method is suitable for implementation in microcomputers. © 1988.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/653321988-01-01T00:00:00Z
- Computer-aided interactive plastic design of frameshttps://scholarbank.nus.edu.sg/handle/10635/65335Title: Computer-aided interactive plastic design of frames
Authors: Alwis, W.A.M.
Abstract: A computer method for analysis and design of plane frames is presented. The method is meant primarily for plastic collapse analysis. Optimal design and elastic-plastic deformation analysis capabilities are provided as options on the same computational platform such that all activities share common internal data structures. A specific feature is the interfacing of user input with analysis calculations, resulting in an interactive design system. Four sequential levels of input data are considered: frame topology, geometry, member sections and loading. Separate calculation modules are activated at each level of input, permitteng interactive data modifications; computational work that needs to be repeated to obtain the new solution is that of the modification level and the following levels if any. © 1993.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/653351993-01-01T00:00:00Z
- Collapse of reinforced concrete grid frameshttps://scholarbank.nus.edu.sg/handle/10635/65309Title: Collapse of reinforced concrete grid frames
Authors: Mansur, M.A.; Alwis, W.A.M.
Abstract: Test results of six reinforced concrete grid frames of four different configurations are presented in this paper. For each frame collapse load analyses have been carried out using two different interaction relationships to represent the behaviour of a section at, collapse: one for combined torsion, bending and, shear and the other by ignoring the effect of shear. The predictions of the collapse load and mode of failure by both the methods have been found to be in good agreement with test results. It has been shown that the effect of transverse shear is only marginal for the grid frames considered in this study.
Sat, 01 Jul 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/653091989-07-01T00:00:00Z
- Should load remain constant when a thin-walled open-profile column buckles?https://scholarbank.nus.edu.sg/handle/10635/66160Title: Should load remain constant when a thin-walled open-profile column buckles?
Authors: Alwis, W.A.M.; Wang, C.M.
Abstract: This paper addresses the fundamental question of whether the applied load should necessarily be assumed to remain constant for bifurcation buckling analysis of thin-walled open-profile columns via the work-energy approach. The constant load condition has been recently used as a fundamental requirement for a valid analysis by Goto and Chen (1989, Int. J. Solids Structures 25, 621-634) to dispute a theory proposed by Ojalvo (1989, ASME J. Appl. Mech. 56, 633-638). This paper establishes that neither constant load nor constant distance need be insisted upon for a valid analysis. It is permissible to assume either constant load or constant distance (or any other compatible configuration with second order changes in loads and distance) for a valid analysis. It is essential to ensure that the appropriate strain energy and work expressions are adopted. © 1994.
Tue, 01 Nov 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/661601994-11-01T00:00:00Z
- Strength of two-way ferrocement slabs containing patch reinforcementhttps://scholarbank.nus.edu.sg/handle/10635/66232Title: Strength of two-way ferrocement slabs containing patch reinforcement
Authors: Mansur, M.A.; Alwis, W.A.M.
Abstract: An experimental investigation into the collapse load behavior of simply supported ferrocement slabs containing a nonuniform distribution of reinforcement is reported. All slabs had identical dimensions and consisted of three reinforcing zones. The distribution of reinforcement in each zone was kept uniform, but the amount was systematically varied by using fine wire mesh in patches. Results of eight square slabs tested under uniform loading simulated by 16 point loads indicate that the collapse load depends not only on the amount of reinforcement, but also on its arrangement. Yield line analysis using finite elements and linear programming has been found to give good predictions of the collapse load and the mode of failure.
Fri, 01 Apr 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/662321988-04-01T00:00:00Z
- Buckling of skew plates and corner condition for simply supported edgeshttps://scholarbank.nus.edu.sg/handle/10635/57979Title: Buckling of skew plates and corner condition for simply supported edges
Authors: Wang, C.M.; Liew, K.M.; Alwis, W.A.M.
Abstract: The paper considers the elastic buckling of skew plates subjected to in-plane loadings. The buckling analysis is performed using the Rayleigh-Ritz method with the newly proposed pb-2 Ritz functions, which consist of the product of a two-dimensional polynomial function and a basic function. The basic function is formed from taking the product of the equations of the boundaries, with each equation raised to the power of 0, 1, or 2 corresponding to free, simply supported, or clamped edges; thus satisfying the kinematic boundary conditions at the outset. With pb-2 Ritz functions, the analyst avoids the difficulty of searching for the appropriate function for any arbitrarily shaped plates with various combinations of supporting-edge conditions. Using this efficient and accurate pb-2 Rayleigh-Ritz method, buckling solutions are obtained and presented in the form of design charts for skew differing viewpoints on the kinematic condition for a corner formed by two simply supported edges are discussed.
Wed, 01 Apr 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/579791992-04-01T00:00:00Z
- Use of engineering strain and Trefftz theory in buckling of columnshttps://scholarbank.nus.edu.sg/handle/10635/66363Title: Use of engineering strain and Trefftz theory in buckling of columns
Authors: Wang, C.M.; Alwis, W.A.M.
Abstract: The elastic buckling of clolumns with allowance for prebuckling axial shortening was analyzed using the engineering strain definition and compared with earlier results that were based on Green strain definition. The governing equilibrium equation becomes slightly different in the sense that the flexural rigidity is factored upward by suared lambda instead of strainght lambda, as in previous studies.
Thu, 01 Oct 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/663631992-10-01T00:00:00Z
- Passive attenuator for shelter protection against explosionshttps://scholarbank.nus.edu.sg/handle/10635/32543Title: Passive attenuator for shelter protection against explosions
Authors: ALWIS, WEERAMUNI A. M.; CHONG, OI YIN M. K.
Abstract: A family of passive attenuators for shelter protection against explosions which reduce the pressure and impulse by combined effects of reflection, expansion, contraction and deviation contributed by the geometry of the attenuator.
Tue, 30 Jul 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/325431996-07-30T00:00:00Z
- Wagner term in flexural-torsional buckling of thin-walled open-profile columnshttps://scholarbank.nus.edu.sg/handle/10635/66395Title: Wagner term in flexural-torsional buckling of thin-walled open-profile columns
Authors: Alwis, W.A.M.; Wang, C.M.
Abstract: This paper considers the Wagner term in flexural-torsional buckling of thin-walled open-profile columns, which has drawn much attention following its rejection by Ojalvo in 1981. During the ensuing debate on the subject, further issues of flexural-torsional buckling were raised highlighting the need for a comprehensive clarification. This paper collates various questions that have not been convincingly answered. In tackling these questions, two simple bar models are first used to clarify important differences between alternative representations of internal stress resultants, and their relationship with the Wagner term. With this background, a statically admissible free-body diagram is described, establishing the Wagner term without resorting to disputed means such as the use of a fictitious lateral load. The Wagner term is shown to be an internal stress resultant of the longitudinal prebuckling forces distributed across the member section; this stress resultant is of the same order of magnitude as the St Venant and warping torque. The spatial effect of stresses contributing to the Wagner term cannot be captured by the single line representation as proposed by Ojalvo.
Thu, 01 Feb 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/663951996-02-01T00:00:00Z