Time-Dependent Analysis of Precast Segmental Bridges

Prestressed segmentally constructed balanced cantilever bridges are often subjected to larger deflections than those predicted by calculations, especially for long-term effects. In this paper, the case of modular balanced cantilever bridges, which are prestressed segmental bridges obtained through a repetition of the same double cantilever, is investigated. The considered bridges are two typical cases of modular balanced cantilever both subjected to large deformations during their lifetime. In this case, due to the unusual employed static scheme, creep deflections indefinitely evolve over time particularly at the end of the cantilevers and in correspondence with the central joint. These remarkable deflections cause discomfort for vehicular traffic and in certain cases can lead to the bridge collapse. Important extraordinary maintenance interventions were necessary to restore the viability of the bridges and to replace the viaduct design configuration. To this aim, the static schemes of the structures were varied, introducing new constraints, new tendons, and carbon fiber reinforcements. In the present work, time analysis was performed to compare the time-dependent behavior of the bridge according to two different creep models, the CEB-FIP Model Code 2010 and the RILEM Model B3, with the real-time-dependent behavior of the bridge observed during its lifetime. The two different employed models exhibit different behaviors in terms of displacements and bending moments acting on the bridge. Interesting considerations are made on their reliability in simulating the long-term creep effects that evolve indefinitely over time. Moreover, retrofitting techniques have been proposed and modeled to predict their effectiveness in reducing time-dependent deflections

IMPA versus Cloud Analysis and IDA: Different Methods to Evaluate Structural Seismic Fragility

Well-known methods for seismic performance assessment, such as incremental dynamic analysis (IDA), multi-stripes analysis (MSA) and the cloud method, involve nonlinear response time-history analyses to characterize the relationship between the chosen damage measure versus intensity measure. Over the past two decades, many authors have proposed simplified procedures or nonlinear static approaches to develop fragility. In these procedures, the capacity of the system is evaluated by nonlinear static procedures (i.e., the capacity spectrum method (CSM), the N2 method, modal pushover analysis (MPA)) and the demand is derived by response spectra. In addition to the familiar ones, incremental modal pushover analysis (IMPA) is a novel nonlinear static procedure proposed in recent years, and it is used in this research to present an IM-based fragility estimation. The accuracy and effectiveness of different methods to assess vulnerability are investigated by comparing fragility curves derived by MPA-based cloud analysis, IMPA and cloud analysis against IDA. The comparison gives valuable insights on the influence of scaling on different sets of records; however, a more extended validation is needed to confirm the obtained results and draw more general conclusions. Results arise from two relatively small bins of record motions differing by ranges of Joyner-Boore distance and scattered in a range of magnitude are presented

Shell-supported footbridges

Architects and engineers have been always attracted by concrete shell structures due to their high efficiency and plastic shapes. In this paper the possibility to use concrete shells to support footbridges is explored. Starting from Musmeci's fundamental research andwork in shell bridge design, the use of numerical formfinding methods is analysed. The form-finding of a shellsupported footbridge shaped following Musmeci's work is first introduced. Coupling Musmeci's and Nervi's experiences, an easy construction method using a stay-inplace ferrocement formwork is proposed. Moreover, the advantage of inserting holes in the shell through topology optimization to remove less exploited concrete has been considered. Curved shell-supported footbridges have been also studied, and the possibility of supporting the deck with the shell top edge, that is along a single curve only, has been investigated. The form-finding of curved shell-supported footbridges has been performed using a Particle-Spring System and Thrust Network Analysis. Finally, the form-finding of curved shell-supported footbridges subjected to both vertical and horizontal forces (i.e. earthquake action) has been implemented

IMPAβ: Incremental modal pushover analysis for bridges

In the present study, the incremental modal pushover analysis (IMPAβ), a pushover-based approach already proposed and applied to buildings by the same authors, was revised and proposed for bridges (IMPAβ). Pushover analysis considers the effects of higher modes on the structural response. Bridges are structurally very different from multi-story buildings, where multimodal pushover (MPA) has been developed and is currently used. In bridges, consideration for higher modes is often necessary: The responses of some structural elements of the bridge (e.g., piers) influence the overall bridge response. Therefore, the failure of these elements can determine the failure of the whole structure, even if they give a small contribution total base shear. Incremental dynamic analysis (IDA) requires input accelerograms for high intensities, which are rare in the databases, while scaling of generated accelerograms with a simple increment of the scaling acceleration is not appropriate. This fact renders IDA, which is by its nature time-consuming, not straightforward. On the contrary, the change of input spectrum required by IMPA is simple. IMPAβ also utilizes a simple complementary method coupled to MPA, to obtain bounds at very high seismic intensities. Finally, the two incremental methods based on static nonlinear and dynamic nonlinear analyses are compared

Curved footbridges supported by a shell obtained through thrust network analysis

After Maillart's concrete curved arch bridges were built before the Second World War, in the second half of the past century and this century, many curved bridges have been built with both steel and concrete. Conversely, since the construction of Musmeci's shell supported bridge in Potenza, few shell bridges have been constructed. This paper explains how to design a curved footbridge supported by an anticlastic shell by shaping the shell via a thrust network analysis (TNA). By taking advantage of the peculiar properties of anticlastic membranes, the unconventional method of shaping a shell by a TNA is illustrated. The shell top edge that supports the deck has an assigned layout, which is provided by the road curved layout. The form of the bottom edge is obtained by the form-finding procedure as a thrust line, by applying the thrust network analysis (TNA) in a non-standard manner, shaping the shell by applying the boundary conditions and allowing relaxation. The influence of the boundary conditions on the bridge shape obtained as an envelope of thrust lines is investigated. A finite element analysis was performed. The results indicate that the obtained shell form is effective in transferring deck loads to foundations via compressive stresses and taking advantage of concrete mechanical properties

Optimal design criteria for form-finding of double-curved surfaces

The development of new digital design tools and fabrication technologies stimulated a large research interest in the design and construction of free-form architecture. Free-form architecture indicates the symbolic act of freeing architecture from the limitations of pure form. During the form-finding process, the priority is on identifying the geometry that enables the optimum force flow within the structure. This study focuses on the problem of the form-finding problem of concrete double-curved surfaces. First, a suitable form-finding optimization framework to optimize shell surfaces based on the surface Stress Density method is established. This framework is based on the use of different software such as Rhinoceros, Grasshopper, and Matlab. The stress density method is chosen because it allows obtaining an optimized shape starting by few parameters: the geometric characteristics of the model, the surface density factor and the magnitude of the load. In a second step, the study is focused on a single panel of the structure. Structural analyses of this panel are carried out using the commercial finite element software SAP2000 to demonstrate that it is a shape resistant structure. Finally, a new production process for concrete double-curved surfaces is presented showing a prototype at a small scale. This process is trying to satisfy the needs of new shapes within architectural design. The proposed solution is the improvement of an existing flexible mould formwork technology and represents the first attempt to reach a reusable, reconfigurable and affordable procedure

Geometrical parametric study on steel beams exposed to solar radiation

A finite element thermal analysis was conducted in this study with the aim of evaluating the influence of the geometrical parameters of steel sections on their thermal response under solar radiation. Four W12 and W24 standard steel beams were investigated under the solar irradiation conditions of a sunny summer day. The finite element analysis was carried out using COMSOL Multiphysics considering the Sun’s movement from sunrise to sunset, reflected radiation from the ground, surface convection of air and long wave radiation as the main boundary thermal loads. The temperature-time variation at different locations in the sections, vertical temperature distributions, temperature gradient distributions and thermal stress distributions were investigated. The results showed that the daily maximum temperatures, temperature variation, temperature and temperature gradient distributions and thermal stresses are influenced by the geometry of the steel section. The flange width and flange thickness were found to be the controlling parameters during the noon hours, while these parameters in addition to web depth control the shading effect during the after-noon. On the other hand, web thickness affects the temperature of webs at sunrise and sunset times. Geometrical ratios like Wf/H, Wf/tf2 and 2Wf/Htf were the most influential parameters on tempera-tures, temperature gradients and thermal stresses of steel beams subjected to solar radiation. The investigated section with the maximum Wf/tf2 value of 0.96 (W12 × 58) recorded the highest top-surface noon temperature, while section W24 × 84 with the lowest Wf/tf2 value of 0.60 exhibited the lowest temperature

Seismic analysis of Fujian Hakka Tulous

The overall earthquake response of Hakka Tulous, traditional earth constructions of the Fujian Province (China) and listed among the UNESCO World Heritage buildings, is investigated. Non-linear static analysis (pushover) with the equivalent frame approach is used. Although some rough approximations are assumed, this approach is well suited to model complex masonry structures, like Tulous. In fact, nonlinear analysis implemented by finite elements or by discrete elements would involve complex models hard to converge and needing long computational time. After carrying out seismic analysis of a Tulou prototype, its failure modes and overall seismic response were evaluated. The Tulou has shown to have good earthquake resistance with respect to the maximum seismic action that can be expected in the Fujian Province

A degrading bouc-wen data-driven model for the cyclic behavior of masonry infilled RC frames

Mechanics-based macro-models are often used to simulate the cyclic response of infilled reinforced concrete (RC) frames. However, these approaches are affected by uncertainties regarding damage and failure mechanisms. Therefore, this contribution proposes a new smooth data-driven model for the hysteresis of infilled RC frames. The infill panel is modeled through a damage-based Bouc-Wen element, which accounts for both pinching and deterioration of the mechanical characteristics. The parameters of the model are calibrated from an experimental data set of cyclic responses of RC infilled frames. Analytical correlations between parameters and geometric and mechanical characteristics of the infilled frame are derived. Blind validation tests are carried out in order to demonstrate the effectiveness of the proposed model