G. M. Samuel Knight

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...

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...

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.

Shear Capacity of Doubly Skinned Composite Beams with Lacings

AbstractThe provision of shear stirrups/connectors is found to enhance the shear capacity of beams, thus preventing the brittle mode of failure. A doubly skinned composite system consists of steel cover plates on either side of infill material that are connected by means of shear connectors. Laced steel-concrete composite (LSCC) is a recently developed doubly skinned composite structural system, which is found to possess high ductility. In this paper, a model to predict the shear capacity of LSCC beams is proposed. Applicability of the model is verified through the experimental response. The performance of LSCC beams in terms of nominal failure shear stress is compared with that of laced reinforced concrete (LRC) beams and steel-concrete composite (SCC) beams with other forms of shear connectors such as through-through and J-hook connectors. Shear capacities of LSCC beams are found to be about 25% more than that of laced reinforced concrete (LRC) beams with a shear span to depth ratio of 2.0, while they a...

Wind Loads on Curved Roofs: Effect of Side Walls

Wind tunnel pressure measurement studies on a rigid model (scale 1:300) of structure with curved roof has been carried out under open and suburban terrain conditions. The external pressures exerted over the roof due to the presence of side walls have been investigated for the following test cases: (i) roof springing from ground level i.e., side wall height, h = 0.0d and (ii) roof at elevated levels i.e., h = 0.15d and 0.29d, where ‘d’ is span of the roof. The model has been instrumented with point pressure taps on the roof and area averaged pressure taps on the gable end wall and sidewalls. In this paper, results pertaining to mean and standard deviation of pressure coefficients, ( pe C and pe C ~ ), at edge and mid arch locations on the roof for typical angles of wind incidence i.e., wind blowing (i) parallel ( = 0 ), (ii) perpendicular ( = 90 ), and (iii) diagonal w.r.t. normal to gable end ( = 45 ) have been presented. Based on the study, it is observed that the centre half and windward region of the roof of the model with h = 0.29d is subjected to high suction than that for model with h = 0, which is due to the presence of sidewall. Further, evaluated values of pe C for wind blowing parallel and perpendicular to the axis of the arch have been compared with values given in codes of practice and the evaluated values are observed to be between two values reported in AS/NZS and ASCE/SEI codes of practice for = 0 and reasonable agreement at windward quarter for = 90 .