A Modal Pushover Analysis Procedure for Estimating Seismic Demands for Buildings

Developed herein is an improved pushover analysis procedure based on structural dynamics theory, which retains the conceptual simplicity and computational attractiveness of current procedures with invariant force distribution. In this modal pushover analysis (MPA), the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by a pushover analysis using the inertia force distribution for each mode. Combining these ‘modal’ demands due to the first two or three terms of the expansion provides an estimate of the total seismic demand on inelastic systems. When applied to elastic systems, the MPA procedure is shown to be equivalent to standard response spectrum analysis (RSA). When the peak inelastic response of a 9‐storey steel building determined by the approximate MPA procedure is compared with rigorous non‐linear response history analysis, it is demonstrated that MPA estimates the response of buildings responding well into the inelastic range to a similar degree of accuracy as RSA in estimating peak response of elastic systems. Thus, the MPA procedure is accurate enough for practical application in building evaluation and design

Case History of Tunnelling Through Claystone

A broad gauge railway line is being constructed by Indian Railways in Himalaya. The total route length is 342kms, out of which about 100km is in tunnels. The tunnelling problem while excavating the Tunnel no.1 of Udhampur-Katra section and being faced currently is discussed in the paper. The D-shaped tunnel passes through thickly bedded, moderately soft, sparsely jointed sandstone, sheared claystones, siltstones and overburden comprising boulders/pebbles in sandy/silty matrix. The support pressure and the deformation were monitored to study the performance of the support system. Due to the presence of swelling minerals in claystone and weak & highly jointed rock formations with high rock cover (313m), the tunnel experienced both swelling and squeezing ground conditions resulting in the buckling of wall supports of steel ribs, cracking of tunnel wall concrete lining at places and floor heaving up to 1.2m. With the deformation of wall supports, the tunnel roof support also deformed. Numerical analysis using FLAC3D has been carried out to study the effectiveness of the support system. The study shows that the tunnel with out any support may have the wall deformations up to 2.76m. On the other hand, with rock bolt and 40cm thick steel fibre reinforced shotcrete (SFRS) support, the wall deformation would reduce to 23cm

Capacity‐Demand‐Diagram Methods Based on Inelastic Design Spectrum

An improved capacity‐demand‐diagram method that uses the well‐known constant‐ductility design spectrum for the demand diagram is developed and illustrated by examples. This method estimates the deformation of inelastic SDF systems consistent with the selected inelastic design spectrum, while retaining the attraction of graphical implementation of the ATC‐40 Nonlinear Static Procedure. One version of the improved method is graphically similar to ATC‐40 Procedure A whereas the second version is graphically similar to ATC‐40 Procedure B. However, the improved procedures differ from ATC‐40 procedures in one important sense. The demand diagram used is different: the constant‐ductility demand diagram for inelastic systems in the improved procedure versus the elastic demand diagram in ATC‐40 for equivalent linear systems. The improved method can be conveniently implemented numerically if its graphical features are not important to the user. Such a procedure, based on equations relating the yield strength reduction factor, Ry , and ductility factor, μ, for different period, Tn , ranges, has been presented, and illustrated by examples using three different Ry ‐ μ ‐ Tn relations

A Modal Pushover Analysis Procedure to Estimate Seismic Demands for Unsymmetric-Plan Buildings

An Erratum has been published for this article in Earthquake Engng. Struct. Dyn. 2004; 33:1429. Based on structural dynamics theory, the modal pushover analysis (MPA) procedure retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric‐plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by non‐linear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each floor level. These ‘modal’ demands due to the first few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally‐stiff and torsionally‐flexible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally‐similarly‐stiff unsymmetric‐plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems)

A Modal Pushover Analysis Procedure to Estimate Seismic Demands for Unsymmetric-Plan Buildings: Theory and Preliminary Evaluation

Based on structural dynamics theory, the modal pushover analysis procedure (MPA) retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric-plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by nonlinear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each floor level. These “modal” demands due to the first few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally-stiff and torsionally-flexible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally-similarly-stiff unsymmetric-plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems)

Direct Displacement‐Based Design: Use of Inelastic vs. Elastic Design Spectra

Direct displacement‐based design requires a simplified procedure to estimate the seismic deformation of an inelastic SDF system, representing the first (elastic) mode of vibration of the structure. This step is usually accomplished by analysis of an “equivalent” linear system using elastic design spectra. In this paper, an equally simple procedure is developed that is based on the well‐known concepts of inelastic design spectra. We demonstrate that the procedure provides the following: (1) accurate values of displacement and ductility demands, and (2) a structural design that satisfies the design criteria for allowable plastic rotation. In contrast, the existing procedure using elastic design spectra for equivalent linear systems in shown to underestimate significantly the displacement and ductility demands. The existing procedure is shown to be deficient in yet another sense; the acceptable value of the plastic rotation, leaving an erroneous impression that the allowable plastic rotation constraint has been satisfied

Evaluation of Bridge Abutment Capacity and Stiffness during Earthquakes

The “actual” capacity and stiffness values of the abutment‐soil systems at the US 101/Painter Street Overpass, determined from its earthquake motions, are used to investigate how abutment stiffness varies during earthquakes and to evaluate current modeling procedures. It is found that the “actual” abutment stiffness may be significantly different during different phases of the shaking and decreases significantly as the abutment deformation increases. The CALTRANS modeling procedure leads to a good estimate of the transverse abutment stiffness and capacity. However, this procedure may overestimate the normal abutment stiffness and capacity by a factor of over two, indicating that the assumed value of 7.7 ksf for the ultimate passive resistance of the soil, used in the CALTRANS procedure, may be too high. The AASHTO‐83 and ATC‐6 procedures lead to an initial estimate of the abutment stiffness that is too high in both directions

Diffuse neonatal hemangiomatosis presenting as congestive cardiac failure - A case report

Infantile hepatic hemangioma has substantial arteriovenous shunting which may lead to cardiovascular compromise and hydrops fetalis. It may present as hepatomegaly since the entire liver is involved in most cases. As mortality is very high, a high index of suspicion is required to make a diagnosis and common complications arising out it, especially in the presence of cutaneous hemangioma. We present a 2-month-old baby born at term presented with features suggestive of sepsis with multiple cutaneous hemangiomas, and on evaluation, there was congestive cardiac failure, which was initially thought of cardiac origin but subsequently came out to be arteriovenous shunting of blood in liver

An Abridged Review of Blast Wave Parameters

In case of blast loading on structures, analysis is carried out in two stages, first the blast loading on a particular structure is determined and second, an evaluation is made for the response of the structure to this loading. In this paper, a review of the first part is presented which includes various empirical relations available for computation of blast load in the form of pressure-time function resulting from the explosion in the air. Different empirical techniques available in the form of charts and equations are reviewed first and then the various blast wave parameters are computed using these equations. This paper is providing various blast computation equations, charts, and references in a concise form at a single place and to serve as base for researchers and designers to understand, compare, and then compute the blast wave parameters. Recommendations are presented to choose the best suitable technique from the available methods to compute the pressure-time function for obtaining structural response.Defence Science Journal, 2012, 62(5), pp.300-306, DOI:http://dx.doi.org/10.14429/dsj.62.114

Myco-Biocontrol of Insect Pests: Factors Involved, Mechanism, and Regulation

The growing demand for reducing chemical inputs in agriculture and increased resistance to insecticides have provided great impetus to the development of alternative forms of insect-pest control. Myco-biocontrol offers an attractive alternative to the use of chemical pesticides. Myco-biocontrol agents are naturally occurring organisms which are perceived as less damaging to the environment. Their mode of action appears little complex which makes it highly unlikely that resistance could be developed to a biopesticide. Past research has shown some promise of the use of fungi as a selective pesticide. The current paper updates us about the recent progress in the field of myco-biocontrol of insect pests and their possible mechanism of action to further enhance our understanding about the biological control of insect pests