Historic masonry buildings often require structural repair or retrofit to attain a satisfactory level of seismic resistance. This paper analyses the effect of externally bonded fibre-reinforced ...polymer (FRP) retrofitting systems on the global seismic response of such buildings in order to achieve the fundamental code-based requirements that refer to the structure's state of damage for a specified limit state. As a case study, a three-storey historic unreinforced masonry (URM) building was selected. The first part of the paper presents an FRP design procedure for determining which vertical structural elements should be retrofitted and to what extent. As a result, six different FRP retrofitting layouts have been selected and analysed with the aid of non-linear static analyses in the second part of the paper. The paper concludes with a cost-feasibility study by introducing a cost-effectiveness index for FRP reinforcement that identifies the effectiveness of an FRP layout by accounting for the amount of retrofitting material used and comparing it with its effectiveness in improving the global seismic resistance.
This paper presents new research in the field of nonlinear static seismic analysis and the N2 method for soil-structure systems. The rationale for this study stems from the inclusion of ...soil-structure systems in simplified displacement-based design methods. The conducted research comprises three parts, including original experimental investigations, the development of numerical models and the validation of results. A new methodology is presented that provides a step-by-step procedure for the implementation of the N2 method on soil-structure systems. Results of a dynamic shake-table test on a simplified scaled structural model founded on compacted dry sand are presented, and a numerical model of the experiment is developed and calibrated with the inclusion of soil-structure interaction effects. This indicates one main significance of this paper, which is the variation between the experimental and the analytical model and how they can be compared. Lastly, a case study was conducted on a numerical model of a 3D steel building. The building was analysed using pushover analysis for a fixed base-case and by considering soil-structure interaction effects. The results of both observed cases were mutually compared and further examined by validating them with nonlinear dynamic analyses. A comparison was conducted considering the inter-story drifts, calculated according to the N2 method and time-history analyses. The results show good agreement when the N2 method is used for buildings on compliant soils. Overall, it was observed that a decrease in the inter-story drifts appears at ground level of the building. This research also provides a framework for future research in the examined field, for instance, on different types of buildings, building typologies and irregularities of the structural system.
Numerical modelling of the soil in seismic design of structures is always a daunting task. The goal of this article is to develop a simplistic numerical modelling technique for shallow founded ...buildings on compliant soils. An existing large-scale experimental research (TRISEE) was used for calibration. The physical model comprised of a rigid square foundation placed on a sand bed connected to a rigid column and was subjected to a dynamic sine loading. The results from the TRISEE experiment are well known and commonly used by researchers in this field, yet none of the numerical studies were conducted considering the loose sand case. Nonlinear link elements and linear springs were used for representing the soil. It was determined that the soil behavior is highly influenced by the stiffness, selected hysteresis model, and the p-y curve. Considering the software limitations, numerical models represent the experimental behavior in a good manner. Based on the results obtained from the experiment, a case study on a steel frame building with SSI effects included was conducted. Considering the results from this research, the authors recommend implementation of SSI effects into the building’s design phase since they exhibit unfavorable impacts on the seismic behavior and can lead to underdesigned structural elements. However, it has to be emphasized that certain limitations exist due to simplified modelling approaches that were used for this research.
The seismic retrofitting measures which are appropriate for buildings belonging to the architectural heritage are limited, since the extent to which such buildings are allowed to be altered is ...severely limited. In the paper the possibilities which exist for the implementation of base isolation in the case of the seismic upgrade of unreinforced masonry (URM) structures belonging to the valuable architectural heritage have been investigated. A new methodology for the modeling of URM buildings, based on an equivalent frame model with plastic hinges, was used for this purpose. A case study involving a typical neo-renaissance masonry building is presented, in which base isolation is implemented, and a comparison is made with the response of the building in its original state. A refined approach for the selection of proper isolation devices is proposed which is based on the nonlinear static (pushover) analysis of such buildings and on the desired level of seismic protection, with reference to the code-based damage limit states. Additionally, the incremental nonlinear dynamic analyses were also applied in order to estimate what increases in seismic safety could be achieved if the employed base isolation system was used in the case of different seismic intensities.
Travel time data and variability of travel times can be used to quantify the network performance as an important aspect of sustainable development in modern cities. We introduce a data collection and ...analysis framework to be employed as an integral part of a neighbourhood sustainability assessment (NSA). The proposed framework performs a targeted selection and evaluation of indicators based on publicly available traffic data, specifically addressing short-term observations of travel times and traffic counts. Entailing a hybrid and modular approach, we demonstrate the applicability of travel time reliability measures by combining different datasets, various variability estimators, and visualisation methods, to advance the interpretation strength of the assessment. Implemented are regression methods based on cosinor models, which allow us to analyse the rhythmic behaviour of travel time trends. These models can be applied to assess the differential rhythmicity among different factors, like route, weather conditions and type of day (i.e., weekend or workday). Further, the same datasets are used to evaluate two reliability metrics, i.e., a travel time index and a planning time index. We demonstrate the application of the suggested framework on several strategic routes associated with three testbed neighbourhoods in Ljubljana, Slovenia. The results show that average travel times and their variations are affected by route, day of the week, and weather conditions, and correlate with vehicles count data. Analyses of rhythmicity give straightforward insights into travel time trends, appropriate for comparative analysis and thus well-suited for use in NSA and monitoring practices. To the best of our knowledge, this work presents the first study quantifying reliability indicators intended for integration with NSA standards.
•Travel time distributions are analysed to formulate indicators for the neighbourhood sustainability assessment (NSA)•We enhance NSA methods based on short-term observations of travel times and traffic counts•Cosinor regression is applied for detection and characterization of rhythmicity of travel times•The interchangeable use and integration of two data sources, Google Direction API and roadway counters, is examined•The study provides recommendations for the straightforward analysis and presentation of travel times and their variability
•Seismic failure mechanisms expressed by a single failure mode interaction surface.•Vertical load variation and zero-moment position affecting the lateral strength of URM piers.•Equivalent frame ...model with N–V failure mode interaction plastic hinges.•Application of the IN2 method for application to URM structures.•Comparison between the IN2 method and IDA for URM.
The paper presents a relatively simple and computationally less demanding technique for the modeling and analysis of regular unreinforced masonry (URM) structures. This technique is based on the equivalent frame approach, and incorporates linear beam elements and the plastic hinge concept. The complex seismic failure mechanism of masonry piers is expressed by a single failure mode interaction surface (an “FMI surface”), taking into account the influence of variation in the pier’s vertical loading, and its bending moment distribution. The effect of the governing mechanical and geometrical parameters which determine the shape of the FMI surface is presented and discussed. For modeling purposes, the ultimate lateral strength of a masonry element is expressed as a section which cuts through the FMI surface. A single failure mode interaction plastic hinge (an “FMI hinge”) for each masonry frame element is introduced by combining specific failure modes, taking into account their minimum envelope. Calculations were carried out using the commercially available computer program SAP2000 Ultimate, and the validity of the proposed modeling procedure was confirmed by means of a comparative analysis of an URM wall assemblage which has already been studied by other researchers, using different modeling techniques and analysis software. The effect of the vertical loading acting on piers was studied, as well as the formation of typical failure mechanisms throughout the structure. The final part of the paper broadens the research to a fictitious 3D URM structure, where the out-of-plane behavior of piers has been considered alongside the standard in-plane failure mechanisms. Results obtained using the incremental N2 method were compared, for a range of ground-motion intensities, with selected results obtained using incremental nonlinear dynamic analysis.
Since, in the case of plan-eccentric, externally-braced, high-rack storage structures made of steel, damage to the central part of the structure can cause damage to the stored goods, and thus higher ...earthquake-induced costs, an investigation has been performed into the seismic performance of such structures. An actual structure was analysed both as a fixed base variant, and as a base-isolated variant. The extended N2 method (pushover analysis) was used, and the results obtained were compared with selected results obtained by nonlinear-dynamic analysis. The response of several different mass-asymmetric structural variants, corresponding to different occupancy levels of the structure, was analysed, and the results obtained are presented as floor plan projection envelopes of the top, relative and base displacements, as well as the storey drifts. An interesting result obtained in the research was that asymmetry can increase the damage in the supporting structure on the flexible side, and that the central part of the rack structure remains in the elastic region only when the eccentricity is small. In fact, from the seismic point of view, full occupancy is not the most critical condition, but rather lower occupancy, which could cause eccentricities ranging up to 10% or 15% of the larger floor plan dimension; this could lead to damage propagation in some of the columns. The application of base isolation has a positive effect on the management of seismic performance, even in the case of higher levels of occupancy and larger mass eccentricities. It is pointed out that an eccentricity of 5%, which is prescribed in Eurocode 8, might not be sufficient in such structural types, and that similar concerns could be present in other types of industrial structures with a similar ratio between live and dead loads.
► Mass eccentricity in storage racks depends on the occupancy level of the structure.► Eccentricities could be larger than the accidental eccentricity prescribed by codes.► The seismic performance has been analysed by static and dynamic nonlinear analyses.► Lower occupancy causes larger eccentricities and is more critical as a full one.► Torsional effects are substantially reduced by application of base isolation system.
The paper examines the seismic response of an existing externally braced steel frame high-rack structure and analyses the effects of mass eccentricities that can be realistically achieved by ...asymmetric positioning of the stored payload. Apart from the symmetric, three different extreme payload distributions with varying occupancy levels have been considered, with the payload mass concentrated: (i) at the topmost part of the structure, (ii) at the upper corner of the structure and (iii) at the outermost edge of the structure. The seismic performance has been analysed by using unidirectional non-linear dynamic analyses as well as by non-linear static analyses, with the structure's response observed in the cross-aisle direction in which it is possible to account for the effects of torsional twist. The results showed that most unfavourable payload eccentricities might increase the seismic risk leading to local instability of the rack columns. From a seismic point of view, a fully occupied structure does not present the most critical condition. It is obtained at an intermediate occupancy level, which allows more space to produce horizontal and/or vertical eccentricities. Very small occupancy levels in turn produce smaller induced seismic forces and might therefore not be of critical concern. The paper concludes that the payload distribution concentrated symmetrically at the topmost part is the most critical for the central part of the rack structure and that concentrating the payload eccentrically at the outermost edge is the most critical for the flexible side of the structure, while shifting the payload to one of the upper corners is generally not of critical concern.
In this study the effects and costs of implementing a base isolation system for the mitigation of the seismic risk of an existing externally-braced steel frame rack structure are analysed by means of ...nonlinear static (pushover) analysis. Various plan asymmetric variants, with different realistic distributions of the payload mass and occupancy levels, have been investigated under two seismic intensities. The results obtained are presented as floor plan projection envelopes of the top displacements and as plastic hinge damage patterns of the superstructure. In the presented cost evaluation, the cost of the implementation of the proposed base isolation system is compared with the estimated costs of structural repairs to the damaged structural members of the superstructure, as well as with estimated expenses of the downtime period and content damage. The results have shown that base isolation is, in general, not economically feasible for lower ground motion intensities, whereas it could be of great benefit in the case of moderate and high intensities. A simple rough cost estimation study, based on the obtained plastic hinge patterns, showed that the inclusion of the downtime period costs and content damage costs might be important parameters, which — if taken into account — could make such an isolation system viable also for lower ground motion intensities. The other benefits brought by seismic isolation, such as savings on the building design costs, reductions in the threat to employees’ lives, and others, were, however, not included in the presented study. The comparison is done only for two deterministic scenarios of seismic attack, e.g. for design ground motion intensity (
a
g
=0.175 g) and for increased intensity with
a
g
=0.25 g indicating the Maximum Considered Earthquake level.
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