N. Lakshmanan

Pressures on a 110 scale model of the Texas Tech Building

Measurements of wind pressures on a one-tenth scale model of the Texas Tech Building in a large wind tunnel are described. The mean and RMS pressure coefficients obtained from the model for critical corner tappings for oblique wind directions, are in excellent agreement with the corresponding full-scale values. The largest minimum pressure coefficients for these tappings are approximately 20% less in magnitude than the corresponding full-scale values. The increased Reynolds number for the present test series is believed to play a significant part in the greatly improved agreement obtained.

Full scale measurements of the structural response of a 50 m guyed mast under wind loading

Abstract Guyed masts are used for wireless communication, meteorological measurements, and recently, even for power transmission. The behaviour of the mast is non-linear due to its slenderness and compliant ‘guy-support’ system. The guys also exhibit non-linear behaviour especially at low values of pretension due to possible multimodal excitations and dynamic response to wind turbulence. This paper presents the results of measured wind characteristics and associated dynamic response of a 50 m tall guyed mast located on the east coast of India in ambient wind conditions. The measured root mean square values of displacements have been compared with a patch load method suggested by Davenport and Spalding [4] . The adequacy of current design practice is reviewed, in the light of the full scale experimental observations.

Failure Analysis of Transmission Line Towers

Transmission line towers, though designed per code provisions, may fail during mandatory testing required in many countries. Different types of premature failures that were observed during full-scale testing of transmission line towers at Tower Testing and Research Station, Structural Engineering Research Centre, Chennai (CSIR-SERC) are studied, and the results are discussed in detail. The failures are modeled using finite-element software, and the analytical results and the test results are compared with various code provisions. The nonlinear finite-element analysis program NE-Nastran was used to model the elastoplastic behavior of towers. Bracing members with slenderness ratios above 170 become ineffective, even though they have to carry insignificant forces. Importance of design assumptions and connection detailing in overall performance of towers were studied. Nonlinear finite-element analysis is useful in understanding the system behavior and for prediction of the failure pattern and ultimate load. B...

A two-degree-of-freedom base hinged aeroelastic (BHA) model for response predictions

Abstract An alternative aeroelastic modelling technique for the response predictions of tall buildings in two fundamental translational modes, namely a two-degree-of-freedom base hinged aeroelastic (BHA) model, is proposed. This modelling technique has all the advantages of the conventional “stick” model in terms of its simplicity and its ability to readily change the mass, stiffness, structural damping and geometry of the building model and also has the ability to model coupled translational–torsional motion (complex motion). It is found that the frequencies of vibration of the BHA model can be accurately predicted by means of a free-standing-cantilever model and the responses of the CAARC standard tall building in the along-wind and cross-wind directions observed by a BHA model are similar to those observed by a conventional “stick” model and other published records.

Priority ranking towards condition assessment of existing reinforced concrete bridges

Existing old bridges in most countries were designed for less traffic and are inadequate to carry current-day traffic and satisfy the present codal provisions. Even for newer bridges, deterioration caused by unforeseen service conditions and deferred maintenance is causing great concern to bridge engineers. Hence, there is an urgent need for a systematic methodology for priority ranking of the bridges for both their rehabilitation in the future and for the allocation of funding. In this paper, an Analytic Hierarchy Process (AHP), which is an efficient decision making tool for complicated problems with multiple evaluation criteria and uncertainty, has been proposed for the condition ranking of reinforced concrete (RC) bridges. Fuzzy logic is used to handle the subjective judgement, imprecision and intuition involved in a bridge inspectors evaluation report. This methodology would certainly help engineers and bridge management policy makers to overcome the problems related to prioritization and decisions on funding related to the rehabilitation of bridges. The background information, the formulation and the details of the computer program developed in this study for the condition ranking of bridges are presented in this paper. The methodology and its application are demonstrated through a case study.

Effect of Bolt Slip on Tower Deformation

AbstractThe analytical deformation of a transmission line (TL) tower computed using software is less than the test deformation. A TL tower consists of many splice joints in the leg member. A small rotation owing to bolt slip in the joint may cause additional deformation in the tower, which is difficult to predict and cannot be accounted for in the analysis. Experimental studies are conducted on variation of bolt force with the applied torque and on bolt slip in butt-jointed specimens and the load at which it occurs. The actual behavior of the joints is studied on seven towers recently tested at the Tower Testing and Research Station of the Structural Engineering Research Centre, a national laboratory under the Council of Scientific and Industrial Research, Government of India. The bolt slip occurs when the axial force in the leg member exceeds the clamping force at that particular joint. On the basis of the studies conducted, a factor that gives the relationship between experimental and theoretical deform...

Seismic performance evaluation of exterior beam-column sub-assemblages designed according to different codal recommendations

In the present study, seismic performance of exterior beam-column sub-assemblages is evaluated by considering different stages of Eurocode (EC) and Indian Standard (IS) provisions for design of the reinforced concrete structures. The study has brought out the implications of the differences in the guidelines on seismic performance. It is found that the gravity load designed (GLD) structure is vulnerable to even medium intensity earthquake. Among the seismically designed specimens without ductile detailing, the one which was designed as per IS exhibits better performance compared to that designed according to the EC with 10% more energy dissipation under large drift ratio. Among the seismically designed and ductile detailed specimens, the one designed as per EC provisions for medium ductility could not perform as good as that designed as per ductile provisions from IS (25% less energy dissipation). Stiffness degradation of the specimens is also found to be a crucial parameter and varies considerably among the specimens. Therefore, earthquake design and ductile detailing provisions of different standards and their progressive improvements have considerable influence on seismic performance of reinforced concrete structures.

Evaluation of Longitudinal Force on a Railway Bridge Based on Strain Measurements

Evaluation of longitudinal force is very important for the performance evaluation of older bridges and for the design of new bridges. There is a growing demand to increase freight haulage in railway networks, in particular, on the iron ore routes of various zones of Indian railways. This proposed alteration may subject the bridges to higher tractive effort/braking forces together with higher axle loads. It is thus obvious that there is a need to check the performance of the concerned bridges under this proposed increased loading. Hence, as part of evaluating the bridges for higher axle loads, experimental investigations have been carried out on a typical steel plate girder railway bridge. This paper gives the summary of experimental investigations, test setups, and results obtained for the evaluation of longitudinal force. The longitudinal force evaluated based on the experiments for the increased axle loads is found to be within the design limits specified. The special fixtures developed for direct measurement of the longitudinal force are found to give the reliable results compared to the strain gage measurements on the girder. The results show that only part of the rail force is transmitted to the girder.

Simplified Approach for Finite Element Analysis of Laced Reinforced Concrete Beams

Laced reinforced concrete (LRC) consists of continuous bent shear lacings along with longitudinal reinforcement on both faces of a structural element. LRC is used to enhance the ductility and provide better confinement of the concrete. However, conventional finite element modeling of structural components made of reinforced concrete (RC)/LRC requires concrete and steel to be considered as separate entities. This paper presents a new simplified approach for finite element modeling of RC/LRC structural elements that are primarily under flexure. In this approach, LRC is considered as a homogenous material and beam elements are used to model the LRC beams. Equations for obtaining the equivalent stress and strain characteristics for equally reinforced LRC beams under flexure are derived, retaining the moment-curvature characteristics. This approach is validated by comparing the results of numerical studies on LRC beams with those of experimental values. The findings indicate that this approach can predict the peak load and ductility factors for LRC beams.

FLEXURAL AND LOCAL BUCKLING INTERACTION OF STEEL ANGLES

The column buckling equation and plate buckling equation are merged to obtain a graphical relation in the elastic and inelastic buckling ranges. This graphical relation has been used to classify all possible modes of hot rolled angle sections investigated by previous researchers in their experimental works. Forced plate buckling experiments have been carried out to verify the graphical relation for plate buckling. Design practices adopted by various standards for design of steel angles, have been compared with respect to this graphical relation and discussed. The importance of width to thickness ratio has been used to emphasize the buckling characteristics of hot rolled angle sections. The objective of this paper is to discuss the plate buckling failures of the angle sections recorded during full scale testing of transmission towers at Tower Testing and Research Station, SERC, Chennai, India. The plate buckling failures in tower testing for the past eighteen years have been analyzed and suggestions are given to avoid such failures in real structures and during testing.