The need for a journal in India, devoted exclusively to activities in the field of structural engineering with special emphasis on research and development had been felt since long. To meet this demand and to provide a medium for structural engineers in India and abroad and to document, discuss and debate current trends in design, research, and development relating to all areas of structural engineering, SERC decided to undertake the publication of a quarterly journal entitled Journal of Structural Engineering (JoSE). The first publication came out in April 1973. From 1993 onwards, the first issue in each Volume has been dedicated to a special topic of current R&D interest. From the year 2005 onwards, the JoSE has been converted in to a bi-monthly Journal to meet the enhanced responses received from the prospective authors, nationally and internationally.
CSIR-Structural Engineering Research Centre
Aluminum foam for protective packaging in comparison with polymeric foams
Metal foams has shown their usage in variety of industrial applications. Such foams are used for protective packaging to prevent the damage in case of impact due to various accidental reasons. Many equipment needs to be transferred from one place to another for several reasons. This may lead to damage of the equipment if being improperly handled or packed. Excessive accelerations during impact may damage the equipment thus indicating the importance of properly chosen packaging material. The present investigation aims for the study of applicability of aluminum foam for protective packaging of delicate equipment in comparison with the commonly used polymeric foams. In the present investigation a circuit board, packed in foam material, is dropped at an angle onto a rigid surface. The mathematical model of packaging, foam and circuit board is developed in finite element software and it is subjected to a simulated drop from a given height to assess the level of protection. The main aim is to assess whether these foam packaging are adequate to prevent circuit board damage when the board is dropped from a particular height.
Impact; aluminum foam; polymeric foam; energy absorption; packaging; finite element analysis.
Copyright (c) 2024 Journal of Structural Engineering
Experimental investigations on seismic performance of corrosion affected gravity load designed reinforced concrete beam column sub-assemblages
Most of the reinforced concrete structures were designed only for gravity loads, even in the regions prone to high seismicity. Though these structures perform well under gravity load cases, their performance under seismic event is still a grey area. In RC structures, beam-column joints are crucial members, to dissipate the seismic energy imparted to the structure. It is evidenced that most of the reinforced concrete structures are severely affected by the corrosion and the performance of those structures under seismic events needs special attention. In view of this, investigations are carried out to evaluate the performance of the gravity load designed (GLD) uncorroded and corrosion affected beam-column sub-assemblages under reverse cyclic loading. The study not only brings out the extreme vulnerability of GLD structures under seismic events, but also points out the further detrimental situation due to corrosion in the RC structures. The findings of the present study will be helpful to formulate the adequate strengthening measures for improved seismic performance of the deficient- and degraded- structures to avoid catastrophic failures under seismic events.
Beam-column; corrosion; strength degradation; stiffness degradation; energy dissipation.
Energy balance assessment of tall buildings equipped with friction dampers for earthquake response control
Seismic analyses and energy balance assessment of a two-dimensional (2D) moment-resistant frame (MRF), a braced frame (BF), and a friction damped frame (FDF) are reported in the present study. The mathematical formulations for various forms of energies in the MRF, BF, and especially in the FDF are presented. These multi-storey steel frames have been modelled with lumped masses on each floor and massless columns in each storey. Four such frames with 5, 10, 15, and 20 storeys are subjected to three different earthquake ground motion time histories to calculate various energies, such as the input energy, energy dissipated in structural damping, energy dissipated by the friction damper, strain energy, and kinetic energy. The results obtained for the MRF, BF, and FDF are assessed to investigate the effectiveness of the friction damper. It is observed that the friction damper dissipates significant amount of energy imparted by the seismic ground motion, which considerably reduces the demand of structural damping in the tall buildings. Furthermore, the kinetic and strain energies in the FDF diminish more rapidly than that in the MRF and BF, which signifies improved seismic performance of the tall buildings equipped with the friction dampers.
Earthquake; energy analysis; energy dissipating devices; friction damper; performance based seismic design.
Seismic control of benchmark cable-stayed bridge using variable sliding isolators
The study of earthquake response of benchmark cable-stayed bridge with different sliding isolation systems is conducted. Considering the phase-II benchmark problem, the selected isolation systems consist of Variable Friction Pendulum System (VFPS), Variable Frequency Pendulum Isolator (VFPI) and Variable Curvature Friction Pendulum System (VCFPS). A comparative performance study of the selected isolators for seismic response control of bridge is carried out. A parametric study is also performed to investigate the effectiveness of the isolators. By varying the different parameters of the isolators, evaluation criteria of the benchmark cable-stayed bridge problem is found out. Using these seismic isolators, significant reduction in base shear, seismic responses are observed. Comparing the values of evaluation criteria presented, it can be deduced that VCFPS and VFPS are more robust than the other sliding isolators considered. The performances of the variable sliding isolators are better than traditional FPS.
Benchmark cable-stayed bridge; VFPS; VFPI ; VCFPS; seismic response; base isolation.
Seismic mitigation of piping system with control devices under tri-directional seismic excitation
Seismic loads on piping system due to an earthquake can cause excessive vibrations, which can lead to serious instability resulting in damage or complete failure. In this paper, passive and semi-active control devices have been studied to mitigate seismic response and vibration control of piping system used in the process industries, fossil and fissile fuel power plant. A study is conducted on the performance of passive and semi-active control devices with the variation in parameters of devices and or with different control algorithms of the damper and subsequently optimum parameter of devices are obtained. The effectiveness of the passive and semi-active control devices in terms of reduction in the responses, namely, displacements, accelerations and base shear of the piping system is investigated by comparing uncontrolled responses under four different artificial earthquake motions with increasing amplitudes. The analytical results are compared with the corresponding experimental results which indicated a good match with the proposed analytical procedure for the X-plate dampers. The analytical results demonstrate that the passive and semi-active control devices under particular optimum parameters are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping systems.
Seismic; passive and semi-active control devices, stiffness ratio; control law; piping systems.
A study on the design parameters of the compliant LCD for structural vibration control under near fault earthquakes
Earthquake ground motions, recorded in near-fault zones, differ from far-field earthquake excitations. The forward directivity effect often results in high magnitude long period pulse(s) in the velocity time history along with large ground displacement. Again, because of the short travel distance, the ground motion is rich in high frequencies. Consequently, both short period as well as flexible structures have very high damage and collapse potential under near-fault earthquake ground motions. Nowadays, the focus of researchers is seismic protection of structures by use of control devices. Amongst the relatively low-cost but reliable and effective passive control devices, the Liquid Column Damper (LCD) has gained ground but it is only applicable to flexible structures. The Compliant LCD (CLCD) is found suitable for short-period structures as well. In this paper, the performance of the CLCD is investigated for SDOF structural systems subjected to both fault normal and fault parallel earthquake motions, including the fling effect. The sensitivity of the damper performance to the CLCD design parameters is examined in detail. The study indicates that the CLCD is capable of acting as a control device for such earthquake vibrations. The results of the parametric study indicate design trends some of which are different from the existing ones for far-field ground motions.
Near-fault earthquake; vibration control; pulse-type ground motion; compliant liquid column damper (CLCD).
Seismic performance of mid-rise RC frame and frame-shear wall buildings designed for Indian codes
The performance-based assessment procedure is utilized in order to study the seismic performance of mid-rise RC frame and frame-shear wall buildings designed for Indian codes. Three 15-storied buildings consisting of frame, frame-shear wall and frame-shear wall core are designed for the same base shear coefficient based on the empirically obtained period of the building as recommended in IS 1893. The RC frame buildings are modeled using the gross section properties, as well as cracked section properties as per ASCE 41 guidelines. In the frame-shear wall and frame-shear wall core buildings, the RC members are modelled using cracked section properties, whereas the shear-wall and shear-wall core are modelled using nonlinear finite elements. It is observed that the buildings designed for the force criterion alone show ‘Immediate Occupancy’ and ‘Collapse Prevention’ performance for DBE and MCE levels of hazard, respectively. This performance improves significantly in case of the buildings designed for force as well as drift criterion of IS 1893, which demonstrate ‘Immediate Occupancy’ performance for DBE level of hazard and ‘Life Safety’ performance for MCE level of hazard.
Frame; shear-wall; shear-wall core; frame-shear wall; seismic performance.
Ductility demand on short-length buckling restrained braces in concentrically braced frames
Steel concentrically braced frames (CBFs) suffer from the strength and stiffness degradations due to the compression buckling of conventional braces during the seismic events. Low-cyclic fatigue fractures associated with these buckling-type braces (BTBs) also reduce the overall ductility of CBFs. In contrast, buckling-restrained braces (BRBs) having symmetric hysteretic response can contribute to the improved energy dissipation and the superior ductility potential prior to fracture. However, the relatively smaller brace stiffness and the preferred pinned connections in buckling-restrained braced frames (BRBFs) results in the increased drift demand that may adversely affect the retrofitting and reusability of the structures after the earthquake. A hybrid brace having a combination of an elastic BTB segment and a yielding short length BRB (SLBRB) segment in series can increase the lateral stiffness of BRBFs, which can reduce the drift response by maintaining the symmetric hysteresis. This may result in the increase in ductility demand in the SLBRB segments of the hybrid brace in proportion with the decrease in the yield lengths. This study is encompassed on the determination of ductility demand requirements in a 3-story braced frame fitted with the hybrid braces arranged in the chevron configurations. Non-linear static and dynamic analyses are conducted on hybrid braced frame (HBF) as well as BRBF. The results of drift response and maximum ductility demand of HBF and BRBF are discussed.
Damage index; median; pushover; vulnerability; fragility.
Simulation of infills for seismic assessment of open ground storey RC frame buildings
Un-reinforced masonry (URM) infilled RC framed buildings with open ground storey are the most common construction practice for modern multi-storey buildings in India. The complex infill-frame interaction under lateral loading makes the modeling and analysis of infilled frame difficult and the general design practice is to treat infills as non-structural elements and their stiffness, strength and interaction with frame is often ignored. The complex behavior of infilled frames gets further complicated when infills are placed irregularly in elevation keeping ground storey open for parking. Indian Standard, like many other national codes, does not provide any explicit guideline for modeling of infills and insight into the anticipated performance of the infilled frames. This paper takes a stock of modelling and controlling design provisions in some of the major national seismic design codes for URM infills and presents a macro model for URM infilled frames. Using the developed model, an analytical study is presented on effect of open ground storey on the seismic performance of RC frame buildings designed and detailed as per amendment of BIS (2002) requiring the beams and columns of the open ground storey to be designed for 2.5 times the design base shear for the corresponding uniformly infilled frame buildings.
URM infills; RC frame; non-linear analysis; seismic design codes; open ground storey.
Control of blast induced vibration of building by pole placement and LQG control algorithm
Application of smart control technology is becoming popular, particularly for a structure exposed to strong wind or seismic excitation. Although a few studies have been carried out to control blast load-induced vibrations of structures, those studies deal with passive control approach such as base isolation through laminated rubber bearings and lead rubber bearings. Past studies have demonstrated that these types of passive isolators become ineffective as they are subjected to huge displacement during strong vibration and often resulting in a permanent deformation. In these cases an effective control of vibration can be achieved by the application of active control approach as has been studied in this paper. Blast induced loading generates high frequency waves having a very short duration with a large amplitude acceleration that excites the high frequency modes of the structure during the forced regime. However, the transient part of the response is governed by the structural low frequency modes. The excitation of high frequency modes increases the peak floor acceleration of the building and thus, increases the vulnerability of the nonstructural components housed in the structure. Subsequent large displacement vibrations may further increase the damageability of such components. In this study, the pole placement algorithm is utilized to control both the displacement and acceleration responses of a four-storey building. For this purpose, a force is applied in real time through an actuator at the ground floor. The results of this study demonstrate that the proposed approach is indeed effective in controlling the responses of the structure.
Blast load; nonstructural components; vibration control; pole allocation; structural response.
Adjacent structures coupled by viscous damper subjected to random excitations
In this paper, the dynamic response of adjacent structures, modeled as single-degree-of-freedom (SDOF) structures connected by viscous damper, under random excitations is investigated. The ground motion is modeled by a non-stationary random process. To study the influence of non-stationary characteristics of ground motion, the non-stationary response of the coupled structure is compared with the corresponding stationary response. An optimum value of the damping coefficient of viscous damper for which mean square relative displacement and mean square absolute acceleration of the coupled structures attain a minimum value is observed. The influence of system parameters such as frequency ratio, mass ratio and intensity of an earthquake on the optimum value of damper damping is investigated. It has been observed that the frequency ratio and intensity of an earthquake have significant effect on the performance of the viscous damper, whereas, the effect of mass ratio is marginal. An explicit expression for the optimum value of damper damping and corresponding response of the connected structures are proposed. These expressions are derived for the coupled structures subjected to the white noise excitation. The expressions may be used for preliminary optimal design of the viscous damper for connected structures.
Random excitation; seismic effect; passive control; viscous damper.
Comparison of damage index and fragility curve of RC structure using different Indian Standard codes
In today’s world there is much talk about seismic vulnerability, its features and the necessity of study. The main problem which is faced in today’s world is knowledge about proper quantification of damage. The response is obtained after the ground motion has been imparted on the structure. Despite making significant progress in the field of seismic design codes for dynamic analysis, there is a lack of progress in the quantification of damage. The damage criterion should include large displacements as well as the effect of repeated cyclic loading. An Energy-based Damage model is used to assess the Damage Index for the structure taking into account the effect of repeated cycles. The present study has been done to carry out the vulnerability analysis of a four-storey RC Moment resisting frame by modified Park and Ang damage model which is then compared by different Indian Standard code for earthquake resistant design. A new damage scale has been proposed for each of the analysis against an individual code. Each of the fragility parameter has been individually calculated in carrying out this analysis. Fragility curve is plotted by calculating the uncertainty and the median values.
An innovative approximate method for analysis of multi-storey building frames for vertical loads
An experimental study on the performance of M100 concrete at elevated temperature
Design of TMD with nonlinear viscous fluid dampers with varying damping for 6-Storey building with two different structural damping
Dampers have become more popular for vibration control of structures, because of their safe, effective and economical design. Tuned mass damper (TMD) is the most popular passive type of control system especially for buildings subjected to earthquake/ high winds. The properties of the TMD required for optimum performance depends on stiffness, mass and damping distribution of the structure/building or their components need to be isolated from vibrations. From experimental results, the optimum parameters such as optimum tuning ratio (f) and optimum damping ratios (ξd) for TMD were derived by two types of analytical formulations. A 6-Storey steel framed building with TMD is modeled in 3D using SAP2000. The 6-Storey building model is reduced to 6 DOF system and optimum parameters of TMD are computed using the methods by two types of formulations. Two analytical formulation are found to give same optimum tuning ratio, but optimum effective damping ratio are found to be differing. With the optimum tuning ratio and the parameters of TMD obtained by the two methods, the damping in TMD is varied using nonlinear viscous fluid dampers (NVFD) for finding the responses of building in X-direction subjected to one near field earthquake excitation (El Centro with PGA of 4.417 m/s²) and two far field earthquake excitations (Northridge, Kobe with PGA of 8.2676 and 8.1782 m/s² respectively) with their PGA normalized to 0.35g. The effectiveness of the TMD in reducing the responses of structures for two different structural damping of 2% and 5% by increasing effective damping of NVFD in TMD from 0.05 to 0.25 is found.
TMD; time histories; optimum tuning parameters; peak responses.
Strength and ductility of RC beams strengthened with ultra high strength cementitious composite overlay
Strength and ductility are the two important parameters for the design of concrete structures to prevent sudden collapse and minimize damage. An experimental investigation was carried out on pre-damaged RC beams strengthened with Ultra High Strength Cementitious Composite (UHSCC) overlay under four point bending. The aim of the present investigation is to evaluate the strength and ductility of the pre-damaged strengthened RC beams with UHSCC overlay. The enhanced strength after strengthening, ductility using deflection and energy based approach, failure modes and load deflection behavior are discussed. It is observed from the experimental findings that UHSCC overlay significantly enhances the load carrying capacity and ductility. Further, it is noted that both deflection ductility and energy based ductility are in good agreement with each other in the present study.
Ductility; strengthening; RC beams; flexural strength; UHSCC overlay.
Cloud technology module for aggregation of survey data of housing and buildings in coastal villages as per IS:15499 towards cyclone disaster mitigation
With the help of advanced forecasting tools and warning systems, the loss of life could be reduced significantly during the recent very severe cyclonic storms “Phailin” (2013) and “Hudhud” (2014), which crossed the east coast of India, in comparison to the previous cyclones of similar intensity. However, the damage to housing/buildings in Indian coastal villages, in proportion to the intensity of the cyclone, is observed to be continuing. CSIR-Structural Engineering Research Centre (CSIR-SERC), Chennai has been carrying out various studies/activities for the mitigation of damage to housing/buildings in coastal villages due to cyclones for the past few decades. Earlier, CSIR-SERC has evolved survey data sheets to collect structural details of housing/buildings for cyclone damage mitigation. Using these data sheets, survey of housing was carried out in a limited number of coastal villages to identify commonly adopted materials and construction practices. Based on which cost-effective retrofit measures for improved resistance to cyclonic winds have been derived by conducting tests at CSIR-SERC. Subsequently, some of these indigenously evolved survey data sheets were standardized by Bureau of Indian Standards (BIS) in 2004 (IS: 15499). In present study, as part of the development of a Decision Support System (DSS) to assess the cyclone vulnerability of housing/buildings in Indian coastal villages, a web service module using the latest ‘CLOUD TECHNOLOGY’ has been developed for the automated aggregation of survey data of housing and buildings as per the standardized Proformae from numerous villages, which are geographically located in different Taluks/Districts/States of Indian Coastal Region. This paper highlights the relevant features of the web service module developed for the aggregation of survey data from Indian coastal regions towards cyclone disaster mitigation.
Cyclones; housing; buildings; damage mitigation; survey proformae; cloud technology.
Development and optimization of fibre reinforced geopolymer concrete using manufactured sand
Demand for natural sand and Ordinary Portland Cement(OPC) in the construction industry has consequently increased resulting in the reduction of naturally available sources and an increase in price. In such a situation manufacture sand(M-sand) can be an economical alternative to the river sand and fly ash has proved to be potential alternative to the OPC. In this paper an experimental study has been carried out to investigate the use of M-sand as 100% replacement to fine aggregate and fly ash as 100% replacement to cement in concrete. Sodium hydroxide and sodium silicate solution are used as alkaline activators. Mean while super plasticizer and extra water were added to get desired workability.The ratio of Na₂SiO₃ to NaOH of 2.5 was adopted throughout the work. In the present investigation, the experimental program has been carried out to optimize the parameters influencing the development of fibre reinforced geopolymer concrete. The factors that influence the compressive strength such as percentage of mass of coarse aggregate, size of coarse aggregate, alkaline liquids to fly ash ratio, percentage of super plasticizer, concentration of NaOH(Molarity), curing temperature, curing time, rest period prior to curing, fibre content have been studied. The mix proportion for geopolymer concrete was designed using rigorous trial and error method. The compressive strength and workability are the two indices which forms the basis for optimizing the parameters. The short-term Engineering properties of hardened geopolymer concrete like compressive strength, split tensile strength and flexural strength were examined at 7, 28 days. The results shows that the there is an increase in split tensile strength and flexural strengths of Geopolymer concrete with fibers was observed compared to Geopolymer concrete(GPC) without fibers where as there is no significant enhancement in compressive strength. This shows that the Geopolymer concrete behaves similar to OPC concrete.
Fly ash; manufactured sand; alkaline liquids; hooked end steel fibers; compressive strength.
Shake table tests of RCC frame building with passive energy dissipation devices
Open ground storey is a typical feature in the modern multi storey constructions in urban India. These buildings are normally not designed as per the earthquake resistant design proposed in the BIS codes. In order to control the vibration response of high rise buildings during seismic events, passive damping devices are most commonly used for energy absorption. Half scale model of two-bays in X-direction, single bay in Y-direction and three storey reinforced concrete frames has been constructed and tested in the shake table up to failure. The seismically damaged RC frame building is locally retrofitted with geopolymer concrete and then it is globally retrofitted using passive energy dissipation device at the ground storey. It is important to study and understand the response of such buildings and make such buildings earthquake resistant based on the study to prevent their collapse. An elasto-plastic device basically a yielding type device that functions on the energy dissipation achieved by way of deforming a metal plate of uniform thickness beyond its yield displacement in the post-elastic region. The natural frequencies of the model with and without dampers are found. Furthermore, seismic responses of the structure with metallic damper are evaluated with different earthquake excitations. This paper discusses about the construction of test specimen, experimental setup, instrumentation and testing. From experimental studies it has been demonstrated that the X-plate yielding type elasto-plastic damper system are effective in improving the seismic performance of the structure.
Seismic performance; reinforced concrete frame; shake table test; yielding type X-shaped elasto-plastic damper.
Effects of rebar on chloride ingress in steel reinforced concrete components
The presence of rebar is of greater importance with respect to chloride ingress into reinforced concrete (RC) structures,as it can influence the spatial distribution of chloride ions to a significant level. The primary objective of this study is to evaluate the non-uniform chloride ingress into concrete, as well as the distribution of chloride around rebar surface, both spatial and temporal variations. The process of chloride ingress into concrete is considered as an interaction between three phenomena, namely: heat transport; moisture transport; and chloride transport. A field equation represents each of these phenomena and subsequent simultaneous numerical solution, using a combined finite element and finite difference scheme, considers their interaction. Further, chloride ingress into RC is investigated by incorporating different parameters such as water-to-binder ratio, concrete cover thickness, and rebar size and location. The spatial and temporal distributions of total chloride content and time-to-corrosion initiation values along the perimeters of rebars not only are considerably affected by rebar sizes and locations but also are non-uniform in nature.
Concrete; chloride; corrosion; finite element method; rebars; steel reinforced concrete.
Abrasion, permeability and acid resistance of high performance self compacting hybrid fiber reinforced concrete using quartz materials
Numerical studies on corroded steel angle members
Steel structures corrode when exposed to the corrosive environment such as marine, industrial and humid and hence the strength of steel structural members reduces. Steel angle sections are widely used in transmission line micro wave towers and their performance is effected as they corrode. This paper presents the numerical studies on uncorroded, corroded and retrofitted angle specimens considered as compression members and are compared with experimental results. The cross sections considered are ISA 70 × 70 × 5mm, 75 × 75 × 5mm and 100 × 100 × 6mm. Numerical studies were also conducted by using ABAQUS finite element (FE) based software and the results of the FE models are validated with that of the experimental studies and presented.
Accelerated corrosion; carbon fiber reinforced polymer; compression strength; retrofitting.
The capacity based design method for eccentrically braced frames: a critical review
Conventional design and numerical analysis of buried cylindrical structure
A cylindrical buried structure made of two precast Reinforced Cement Concrete (RCC) sections is designed by the conventional method given in Indian Standard (IS) codes. This cylindrical structure is designed as a non-pressure circular RCC pipe. The superimposed load on the structure is high, hence, the strength of standard circular pipe section is increased by taking more wall thickness, higher grade of concrete, extra reinforcement, addition of steel fibres, etc. This cylindrical concrete structure is tested for earth pressure and it was observed that strains and deflections produced in the sections were low. This cylindrical pipe structure is analysed using a two dimensional finite element analysis software package to find out the actual strength of the sections. Detailed numerical analysis of RCC section is given in this paper. In this analysis, various parameters like tensile strength of concrete, soil properties, interfacial contact conditions etc. are changed to check their effects on the results. The results obtained from design using IS code methodology, experimental testing and the numerical analysis using finite element software package are presented in this paper.
Buried cylindrical structure; numerical analysis; soil – structure interaction; duncan - selig soil model; LRFD method; incremental construction technique.
Effectiveness of simple intuitive formulation to predict thermal post-buckling behavior of symmetric linearly tapered columns
Evaluation of thermal post-buckling behavior of heated slender, symmetric, linearly tapered columns, is demonstrated by using a simple intuitive formulation which requires only the mechanical equivalent of the thermal buckling, and the tensile loads, induced in the tapered columns, respectively. Thermal buckling occurs because of the induced compressive load due to the temperature rise from the stress free temperature, when the ends of the tapered columns are constrained to move axially. When the deflections are moderately large, the axial strain-displacement relation becomes nonlinear (von-Karman type). Hence, a tensile load is induced in the column while bending, as a result of the axial boundary conditions, due to the stretching of the neutral axis. Symmetric hinged-hinged and clamped-clamped linearly symmetric tapered columns are considered in this study, so that the structural system becomes completely symmetric. Numerical results in the form of the ratios of thermal post-buckling to buckling loads, varying with the taper and central deflection ratios, obtained from the intuitive formulation, are presented for tapered columns, with the aforementioned boundary conditions. The results match well with those obtained by the Rayleigh-Ritz method, establishing the effectiveness of the intuitive formulation.
Thermal Buckling; thermal Post-buckling; intuitive formulation; Rayleigh-Ritz method; heated columns; symmetric linear tapered columns.
Seismic fragility analysis of pile supported wharf using linear time history analysis
Ports and harbors are considered as lifeline structures because of the significant role they play in transporting people and cargos cost effectively. Currently in India, no guideline is available for seismic design of Port structures and hence vulnerability analysis of such structures becomes essential. Seismic fragility analysis, in terms of fragility curves; represent the probability that the structural damage of a structure, under various levels of seismic ground motions, exceed specified damage states. In present study, seismic fragility curves are developed for an existing pile supported wharf at Mundra port, Gujarat, India. The selected site is in seismic zone V with MCE as 0.36g (IS:1893 part-I, 2002). SAP 2000 is used to create structural model of wharf along with Winkler model to represent soil pile system, in which the pile and soil is symbolized by beam elements and springs respectively. Pushover analysis is performed on the model to find the capacity of wharf. Damage states – serviceable, repairable, near collapse and collapse; are established as per PIANC (PIANC, 2001). Site specific spectra is created using geotechnical report along with ASCE7-05 and correspondingly 10 seismic events are selected, normalized and scaled to 0.1g,0.2g,…1.0g to represent demand. Using linear time history analysis, maximum displacements at deck are obtained and response matrix is created. Based on the damage states and the response matrix, the fragility curves of the wharf are constructed with statistical analysis, using Microsoft Excel. It is revealed that the variation in PGA for DBE, at selected site, as per ASCE7-05(0.883g) and IS: 1893-2002 (0.18g), is nearly 400 % with respect to IS: 1893-2002, which demands the need for revision in the available standards. As per IS: 1893-2002 for MCE(0.36g), the probability of structure entering into repairable, near collapse and collapse state is 100%, 18% and 5% whereas PGA obtained at site for MCE (1.325g), states the probability as 100% for all states, which demands retrofitting the structure to resist future earthquakes.
Seismic fragility analysis; pile supported wharf; site specific spectra; time history analysis.
Flexural strength of polyester fiber reinforced hybrid ferrocement hollow slabs
An analytical model was developed for the flexural strength of hybrid ferrocement hollow slabs cast with alkali resistant polyester fibers mixed in the cement mortar matrix and was validated by the experimental results. Fifteen ferrocement hollow slabs of 2m span were cast and tested in this investigation. The slabs were subjected to one way cyclic loading by applying two line loads at one-third span and tested under simply supported condition and the ultimate moment of the slab was determined experimentally. The “all tensile reinforcement yielding method” was used to determine the flexural strength of the hybrid slabs analytically. The short discontinuous fibers introduced in the cement mortar matrix act as secondary reinforcement reducing the propagation of cracks by the bridging forces. The bridging force contributed by the polyester fibers in the cement mortar matrix was taken into account for the calculation of the depth of the compressive stress block. Also a modification factor ‘v’ (nu) was introduced to find the compression force in the stress block. The flexural strength of the hybrid slabs was found taking into account the bridging forces of the fibers in the tensile zone. The analytical results of the flexural strength of the hybrid slabs are close to the experimental values and it is established that the value of the factor ‘ν’ is validated.
Hybrid ferrocement hollow slabs; analytical model for flexural strength; one way cyclic loading; bridging forces; polyester fibers; all tensile reinforcement yielding method.
Performance of extruded polyester fiber reinforced concrete
The present work deals with the results of experimental investigations on extruded polyester fiber reinforced concrete. Effect of these fibers on various strengths of concrete are studied. Fiber content varied from 0.5 % to 5 % by weight of cement. Various strengths considered for investigation are compressive strength, flexural strength, split tensile strength and the bond strength. Cube of size 100 mm for compressive strength, beams of size 500 mm × 100 mm × 100 mm for flexural strength and cylinders of size 100 mm (diameter) × 200 mm (length) were cast to determine split tensile strength. All the specimens were water cured up to 7 and 28 days and tested subsequently. The workability was measured with the slump cone test. The wet and dry densities at 7 and 28 days were obtained. The static and dynamic moduli of concrete were determined. A comparison of results of extruded polyester fiber reinforced concrete with that of normal concrete showed the improvements in various strengths. The Poisson’s ratio is found to vary within the specified limits.
Synthetic fibers; polyester fibers; FRC; plasticizer; workability; strengths; elastic constants.
Continuous retardation spectrum for basic creep of concrete
Continuous retardation spectrum is a more generalized representation of viscoelastic behavior of linear viscoelastic materials. In this study, an attempt is made to develop continuous retardation spectrum corresponding to different models for predicting basic creep of concrete, namely, the adaptive link mechanism-based model,B3 model and B4 model. The continuous retardation spectrum is approximated using the Post-Widder formula for inverse Laplace transform. The continuous retardation spectra is developed for two concrete mixes, for which basic creep test results are reported in the literature.The compliance values at different times obtained from the continuous retardation spectra are compared with the experimental values. The satisfactory agreement suggests that the continuous retardation spectrum can be used for representing basic creep of concrete.
Concrete; basic creep; continuous retardation spectrum.
Experimental evaluation of crack depth in concrete specimens using time-of-flight technique