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1.
Estimating seismic demands on structures, to predict their performance level with confidence, requires explicit consideration
of the structural inelastic behaviour: to this end, the use of nonlinear static procedures is inevitably going to be favoured
over complex nonlinear time-history methods.
The currently available assessment procedures have been tested predominantly against building frames. A newly derived assessment
procedure is proposed within the scope of bridge applications, based on an innovative displacement-based adaptive pushover
technique. The procedure, which can be incorporated into a performance-based engineering philosophy, is applicable to MDOF
continuous span bridges with flexible or rigid superstructures, and for varying degrees of abutment restraint.
As a first application to determine the viability of the proposed procedure, a parametric study is conducted on a ensemble
of bridges subjected to earthquake motion. It is shown that, compared to the seismic demand estimated by means of the more
accurate nonlinear dynamic analysis tool, the novel static assessment method can lead to the attainment of satisfactory predictions,
both in terms of displacement as well as moment demand on members. 相似文献
2.
When μ is smaller than Routh’s critical value μ
1 = 0.03852 . . . , two planar Lyapunov families around triangular libration points exist, with the names of long and short
period families. There are periodic families which we call bridges connecting these two Lyapunov families. With μ increasing from 0 to 1, how these bridges evolve was studied. The interval (0,1) was divided into six subintervals (0, μ
5), (μ
5, μ
4), (μ
4, μ
3), (μ
3, μ
2), (μ
2, μ
1), (μ
1, 1), and in each subinterval the families B(pL, qS) were studied, along with the families B(qS, qS′). Especially in the interval (μ
2, μ
1), the conclusion that the bridges B(qS, qS′) do not exist was obtained. Connections between the short period family and the bridges B(kS, (k + 1)S) were also studied. With these studies, the structure of the web of periodic families around triangular libration points
was enriched. 相似文献
3.
The average risk of a bridge over water in the USA collapsing from scour during its 75 years design life is estimated at 3.7×10?3. This risk makes scour of foundations the number one cause of bridge collapse and 3 times larger than the next cause of bridge collapse, which is collisions. The current paper presents a site specific method to estimate the probability that a certain scour depth will be exceeded during the life of a bridge. The methodology is limited to some uncertainties associated with the randomness of hydrologic conditions. It does not include uncertainties associated with other input parameters, such as geometry and soil erodibility or uncertainties associated with the scour prediction model. The SRICOS–EFA method is used as the reference method to predict the scour depth. This method requires three inputs: the hydraulic parameters (e.g. velocity hydrograph), the geometry parameters (e.g. pier size) and the soil erodibility parameters (e.g. erosion function). The input is used together with the program to generate the scour depth versus time over the period of interest. The final scour depth is that reached at the end of the specified period. This paper proposes a probabilistic framework to present the final scour depth as a cumulative density function. The cumulative density function of the flow is sampled randomly to give a future hydrograph, which has the same mean and standard deviation as the original hydrograph. For this synthetic hydrograph a final scour depth is obtained by using SRICOS–EFA. Thousands of equally likely hydrographs are generated and the corresponding final scour depths are organized in a distribution. That final scour depth distribution gives the probability that a chosen scour depth will be exceeded. 相似文献
4.
Ioannis F. Moschonas Andreas J. Kappos Panagiotis Panetsos Vissarion Papadopoulos Triantafyllos Makarios Pavlos Thanopoulos 《Bulletin of Earthquake Engineering》2009,7(2):439-468
This study focusses on the estimation of seismic fragility curves for all common bridge types found in modern greek motorways.
At first a classification scheme is developed in order to classify the existing bridges into a sufficient number of classes.
A total of 11 representative bridge classes resulted, based on the type of piers, deck, and pier-to-deck connection. Then
an analytical methodology for deriving fragility curves is proposed and applied to the representative bridge models. This
procedure is based on pushover analysis of the entire bridge and definition of damage states in terms of parameters of the
bridge pushover curves. The procedure differentiates the way of defining damage according to the seismic energy dissipation
mechanism in each bridge, i.e. bridges with yielding piers of the column type and bridges with bearings (with or without seismic
links) and non-yielding piers of the wall type. The activation of the abutment-backfill system due to closure of the gap between
the deck and the abutments is also taken into account. The derived fragility curves are subjected to a first calibration against
empirical curves based on damage data from the US and Japan. 相似文献
5.
An artificial neural networks (ANN) model is developed to study the observed pattern of local scour at bridge piers using an FHWA (Federal Highway Administration) data set composed of 380 measurements at 56 bridges in 13 states. Various ANN estimates of observed pier scour depth on different choices of input variables are examined. Reducing the number of variables from 14 to 9 has negligible effect on the coefficient of determination, R2, (0.73 vs. 0.72). Further sensitivity analysis indicates that pier scour depth can be estimated using only four variables: pier shape and skew, flow depth and velocity with a coefficient of determination of 0.81, suggesting that inclusion of some variables actually diminishes the quality of ANN predictions of short term observed pattern of scour. The ANN estimates indicate that flow depth and flow velocity make up 66% of the coefficient of determination. 相似文献
6.
The dynamic response of vehicular overpasses with massive foundations built in highly populated earthquake prone regions is studied to assess the massive foundation potential of being a technically sound mean to reduce the structural response during major earthquakes. The study consists on numerical simulations using 3-D finite element models. Two typical supports of a major 23 km long vehicular overpass recently built in the north east part of Mexico City valley were considered in this research. This zone is characterized by the presence of stiff soils comprised by dense and very dense silty sands and sandy silts, randomly intercalated by stiff clays layers of variable thickness. Initially, a conventional raft foundation structurally connected to four precast closed-end concrete piles was considered. Then, the potential beneficial effect of a massive foundation of variable depth was assessed. Sets of 3-D finite element models were developed and the response of the systems was evaluated for a typical seismic scenario such as that prevailing at the zone, assuming a potential 8.1 Mw seismic event, and for a hypothetical 8.7 Mw extreme event. Important attenuations of about 39% to 48% at the upper deck spectral accelerations and of 21% to 30% in maximum lateral foundation displacements were achieved with the massive soil improvement for the cases analyzed. Thus, the massive foundations seem to be a convenient alternative to reduce the overall structural seismic response. 相似文献
7.
连续梁桥减震、隔震体系非线性地震反应分析 总被引：23，自引：1，他引：22
本文采用微分型滞回恢复力模式代表桥梁减震,隔震支座的滞回,耗能特性,结合Ｗｉｌｓｏｎ－θ法和四阶Ｒｕｎｇｅ－Ｋｕｔｔａ法编制了桥梁减震,隔震体系非线性地震反应分析程序,并利用程序结合算例分析了减震,隔震支座对连续梁桥的减震效果。 相似文献
8.
A laboratory study of local scour at complex piers under steady clear-water conditions is presented. The term complex piers is used to define a bridge pier comprising of a column, pile cap, and pile group. Comprehensive data over the full range of possible pile cap elevations for complex piers with different geometries were obtained using five complex pier models, which were scaled down from existing bridges in Malaysia. The data are used to evaluate existing methodologies for characterizing the effective width of complex piers with varying pile cap location relative to the undisturbed streambed. The effect of pile cap location on scour depth is also addressed. To improve the predictions of local scour at complex piers, the new data and some previous data are used to propose a new method to predict local scour depth at complex piers. 相似文献
9.
Direct displacement-based design of seismically isolated bridges 总被引：1，自引：1，他引：0
A Displacement-Based Design (DBD) procedure for bridges equipped with different seismic Isolation Systems (IS’s) is proposed.
It has been derived from the Direct DBD method recently developed by Priestley and co-workers. The key aspect of the proposed
procedure is the definition of a uniform target displacement of the deck, which is assigned by the designer to accomplish
a given performance level, expressed through limit values of the maximum IS displacement and of the pier drift, respectively.
The proposed design procedure has been developed for four different idealized force-displacement cyclic behaviours of IS’s,
which can be used to describe the response of a wide variety of IS’s, including: (i) Lead-Rubber Bearings (LRB), (ii) High-Damping
Rubber Bearings (HDRB), (iii) Friction Pendulum Bearings (FPB), (iv) Combinations of either Low-Damping Rubber Bearings (LDRB)
or FPB and Viscous Dampers (VD), (v) Combinations of lubricated Flat Sliding Bearings (FSB) and LDRB, (vi) Combinations of
FSB and Steel Yielding Devices (SYD), (vii) Combinations of FSB, Shape Memory Alloy (SMA)-based Re-centring Devices and VD.
In the paper, the background and implementation of the design procedure is presented first, then some validation studies through
nonlinear time-history analyses on different configurations of continuous deck and multi-span simply supported deck bridges
are illustrated. 相似文献
10.