David P. Thambiratnam

Free vibration analysis of beams on elastic foundation

Abstract A simple finite element method is developed and applied to treat the free vibration analysis of beams supported on elastic foundations. The entire analysis is programmed to run on a microcomputer and with few elements modelling the beam, gives quick and reliable results. Numerical examples pertaining to the free vibration of beams in some special situations are considered, such as a stepped beam on an elastic foundation, beam on a stepped elastic foundation and a continuous beam on an elastic foundation. Present results compare very well with those obtained from existing solutions, wherever possible.

Analysis of Plate Resting on Elastic Supports and Elastic Foundation by Finite Strip Method

Abstract A procedure incorporating the finite strip method together with spring systems is proposed in this paper for treating plates on elastic supports. The spring systems can simulate different elastic supports, such as elastic foundation, line and point elastic supports, and also mixed boundary conditions. To illustrate the application of this procedure, two numerical examples are presented. A three-span simply supported plate is first considered and the effects of support stiffness on the static and free vibration responses and on the critical buckling stress are discussed. A plate resting on Winkler elastic foundation is next studied and the effects of dimension ratio on the static and free vibration responses are discussed. Numerical results show that the spring system can successfully simulate different kinds of elastic supports.

Development of an analytical model for treating bridge-vehicle interaction

In order to check the capacity of existing bridges to heavier traffic and for proper design of new bridges, bridge engineers require improved analytical techniques which consider bridge-vehicle interaction. This paper treats the development of such an interaction model incorporating the dynamic effects of moving vehicles. The bridge superstructure is idealised as a two-dimensional grillage, while the three-dimensional vehicle model has 7 degrees-of-freedom and is capable of accommodating both roll and pitch. The proposed system enables the bridge to be excited by an asymmetric forcing action. The entire procedure for the interaction of the bridge-vehicle system is implemented as an anlytical computer package, able to investigate the influences of various parameters which contribute to the behaviour of a bridge-vehicle system.

Deflection response of plate on Winkler foundation to moving accelerated loads

In this research work, a procedure incorporating the finite strip method, together with a spring system has been developed and applied to treat the response of rectangular plate structures resting on elastic foundation. The dynamic response to moving accelerated point loads is investigated and the effects of initial moving velocity, acceleration and initial load position on the response are discussed. Results indicate that the initial velocity and acceleration have influence on the dynamic response. Response of the plate away form the boundaries resembles that of an infinite plate and might have practical applications.

Cyclic behaviour of concrete filled steel tubular column to steel beam connections

An experimental investigation into the behaviour of composite column-to-beam connections using ten large-scale connections has been conducted, four under monotonic loading and six under cyclic loading. This paper presents the details and results of the six cyclic tests. Details and results from the monotonic tests are reported in a companion paper. All connections consisted of a concrete-filled steel tube (CFST) column (circular), a compact universal beam section and a shop fabricated connection stub. Monotonic testing was first carried out and the results, were used to conduct the cyclic tests. Each specimen tested cyclically had the same general form, consisting of a direct connection of the beam to the tube wall (using flange connection plates, and web cleat plates) and reinforcing bars welded to the top and bottom flanges, embedded into the concrete core. It was found that provided the connection to the face of the column had the capacity to force the hinge into the beam itself, the specimen behaved in a very stable fashion, and achieved ductility levels which were only limited by the beam and the nature of the test itself.

Free vibration analysis of bridges

Most bridges are designed using a static analysis, adjusted by a dynamic amplification factor which is a function of the first flexural frequency. This method is imprecise but continues to be used, partly because of the apparently complex processes required to estimate accurately and to provide for the levels of vibration in a bridge. This paper investigates the natural frequencies and associated mode shapes of bridge superstructures. It compares field observations with theoretical idealizations and finds that, while a single beam idealization is accurate for straight, nonskewed bridges and for some continuous superstructures, many other bridges require an eigenvalue analysis of a finite beam element grillage. A simplified method for estimating the natural frequency of vibration is developed. An application of the Rayleigh method to a grillage model of the bridge, it is quick to apply and accurate to within 10%. The paper also compares the effects of using the static and dynamic moduli of elasticity of concrete in estimating the natural frequency of vibration, and concludes that the dynamic modulus is more appropriate. Finally, it debates the significance of certain types of support stiffness in estimating the fundamental frequency, and finds that their effect is negligible.

DYNAMIC SIMULATION AND ENERGY ABSORPTION OF TAPERED TUBES UNDER IMPACT LOADING

Abstract This paper investigates the energy absorption response of straight and tapered rectangular tubes under axial impact loading using dynamic finite element techniques. The parameters in the study are the number of tapers, taper angle, wall thickness, impact velocity and impact duration. The results show that tubes with three tapered sides have the highest energy absorption capacity, followed by straight tubes and tubes with four tapered sides. Impact velocity has less effect on the absorbed energy for tapered tubes compared with straight tubes. Furthermore, the amplification of absorbed energy with increasing velocity can be controlled using the number of tapered sides. Finally, it was found that tapered tubes have a higher crush force efficiency than straight tubes. Overall, the results highlight the advantages of using tapered tubes for impact energy absorbers such as in crashworthiness applications. The research findings can be used to quantify energy absorption in the design of energy absorbers for impact applications.

Application of foam-filled conical tubes in enhancing the crashworthiness performance of vehicle protective structures

This paper treats the feasibility of including a supplementary energy-absorbing device in the form of foam-filled conical tubes onto vehicular protective structures to enhance their energy absorbing capacity and hence to enhance safety for the occupants during accidental impacts. The effect of the supplementary energy absorber device was investigated for varying values of the wall thickness of the tube and the foam density of the filler. Research findings have shown the inclusion of this supplementary energy-absorbing device to be a cost-effective and beneficial solution, which promoted an enhanced level of occupant safety by enhancing the energy absorption, reducing the amount of plastic deformation sustained by the protective structure as well as reducing the severity of the peak decelerations transferred to the occupant compartment during such an event.

Correlation-Based Damage Detection for Complicated Truss Bridges Using Multi-Layer Genetic Algorithm

The study presents a multi-layer genetic algorithm (GA) approach using correlation-based methods to facilitate damage determination for through-truss bridge structures. To begin, the structures damage-suspicious elements are divided into several groups. In the first GA layer, the damage is initially optimised for all groups using correlation objective function. In the second layer, the groups are combined to larger groups and the optimisation starts over at the normalised point of the first layer result. Then the identification process repeats until reaching the final layer where one group includes all structural elements and only minor optimisations are required to fine tune the final result. Several damage scenarios on a complicated through-truss bridge example are nominated to address the proposed approachs effectiveness. Structural modal strain energy has been employed as the variable vector in the correlation function for damage determination. Simulations and comparison with the traditional single-layer optimisation shows that the proposed approach is efficient and feasible for complicated truss bridge structures when the measurement noise is taken into account.

Computer analysis of column base plates

A three-dimensional finite element analysis using a special purpose programme (FEABOC) has been carried out on column base plates under axial loads and moments. Parameters in the study are the plate thickness and eccentricity of load. Strain distributions in the plate have been determined and the effects of the parameters studied. Results agree reasonably well with those obtained experimentally.