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

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 Review of Fixed Bed Gasification Systems for Biomass

The gasification of biomass into useful fuel enhances its potential as a renewable energy resource. The fixed bed gasification systems are classified as updraft, Imbert downdraft, throatless downdraft, crossdraft and two stage gasifiers. Updraft gasifiers are suitable for gasification of biomass containing high ash (up to 15 %) and high moisture content (up to 50 %) and generate producer gas having high tar content (50–100 g/Nm3). The high temperature (830 oC) air gasification of biomass in updraft gasifiers increase the lower calorific value of producer gas and reduce the tar content. The updraft gasifiers have been used for gasification of bark, wood blocks, chips and pellets, straw, maize cobs, refuse derived fuel (RDF), and waste pellets with air and O2 as the gasifying media. The Imbert downdraft gasifiers are suitable to handle biomass fuel having ash and moisture content less than five per cent and 20% respectively. Modifications in the design of grate and hopper of Imbert downdraft gasifiers have been suggested to gasify non-woody biomass such as coir dust, cotton stalks, wheat straw, hazelnut shells, leather residues, sludge etc. Downdraft gasifiers yield producer gas with lower tar content (1-2 g/Nm3) than updraft gasifiers. Throatless downdraft gasifiers have been developed to overcome the problems of bridging and channelling in Imbert downdraft gasifiers. The throatless gasifiers have been successfully used for gasification of rice husk, wood chips, bagasse, sugarcane leaves, coconut shells etc. Improving the insulation of the gasifier, re-circulation of producer gas and varying the air distribution have been reported to enhance the performance of the throatless gasifiers and reduce the tar content to 50–250 mg/Nm3. In two stage gasifiers, pyrolysis and gasification of biomass takes place in separate chambers resulting in low tar (15–50 mg/Nm3) producer gas. Some aspects of the research and development in fixed bed gasification of biomass and their commercial applications are reviewed and cited in this paper

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

Evaluation of NSP to Estimate Seismic Deformation: SDF Systems

Investigated in this paper is the approximation in the ATC-40 nonlinear static procedure (NSP) that the earthquake-induced deformation of an inelastic single-degree-of-freedom (SDF) system can be estimated by an iterative method requiring analysis of a sequence of equivalent linear systems. Several deficiencies in the ATC-40 Procedure A are demonstrated. This iterative procedure did not converge for some of the systems analyzed. It converged in many cases, but to a deformation much different than dynamic (nonlinear response history or inelastic design spectrum) analysis of the inelastic system. The ATC-40 Procedure B always gives a unique value of deformation, same as that determined by Procedure A if it converged. These approximate procedures underestimate significantly the deformation for a wide range of periods and ductility factors with errors approaching 50%, implying that the estimated deformation is about half the ‘‘exact’’ value. Surprisingly, the ATC-40 procedures are deficient relative to even the elastic design spectrum in the velocity-sensitive and displacement-sensitive regions of the spectrum. For systems with a period in these regions, the peak deformation of an inelastic system can be estimated from the elastic design spectrum using the well-known equal displacement rule. However, the approximate procedure requires analyses of several equivalent linear systems and still produces worse results

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

Status and conservation of avian fauna of Sultanpur National Park Gurgaon, Haryana (India)

The present study was conducted in Sultanpur National Park Gurgaon, Haryana (India) from February, 2011 to January, 2012 to analyze the avian diversity along with its status and abundance. During the study period, a total of 113 species of birds belonging to 14 orders, 35 families and 80 genera were identified. Maximum 41 species belonging to 12 families of order Passeriformes represented 36.28% of the total identified avian fauna while Podicipediformes and Strigiformes were the least represented avian orders (0.88%) with one species each,namely, Little Grebe, Tachybaptus ruficollis and Spotted Owlet, Athene brama respectively. Out of total reported 113 species, 64 were ‘resident’ species and 49 were ‘migrant’ species. Most of the migratory species were winter visitors except Red throated flycatcher, Ficedula parva; Orange Headed Thrush, Zoothera citrine and Eurasian Golden Oriole, Oriolus oriolus which were summer visitors. In all, 42 species were ‘common’, 33 species were ‘uncommon’ and 38 species were ‘occasional’ bird species. Based on sighting, White Breasted Kingfisher, Halcyonsmyrnensis; White Breasted Water Hen, Amaurornis phoenicurus; Common Moorhen, Gallinule chloropus; Black Wing Stilt, Himantopus himantopus; Red Wattled lapwing, Vanellus indicus; Cattle Egret, Bubulcus ibis and Indian Pond Heron, Ardeola grayii were common wetland bird species of Sultanpur National Park while Pied king fisher, Ceryle rudis and Coppersmith Barbet, Megalaima haemacephala were ‘rarely sighted’ bird species. During the study period, 7 ‘globally threatened’ species, namely, Painted Stork, Mycteria leucocephala; Black neck Stork, Ephippiorhynchus asiaticus; Black headed Ibis, Threskiornis melanocephalus; Darter, Anhinga melanogaster; Pacific Reef Egret, Egretta sacra; Sarus Crane, Grus antigone alongwith Hogson bushchat, Saxicola insignis were also recorded from the study area