For engineering systems having a potential for degradation under cyclic loading (e.g., landslides, soil profiles subject to liquefaction, some structural systems), the characterization of seismic demand should include the amplitude and duration of strong shaking within the system. This article is concerned with significant-duration parameters, which are defined as the time interval across which a specified amount of energy is dissipated (as measured by the integral of the square of the ground acceleration or velocity). We develop ground-motion prediction equations for significant-duration parameters as a function of magnitude, closest site-source distance, site parameters that reflect shallow geologic conditions as well as deep basin structure, and near-source parameters. The relations are developed using a modern database and a random-effects regression procedure. We find significant duration to increase with magnitude and site-source distance (effects that had been identified previously), but also to decrease with increasing shear-wave velocity of near-surface sediments and to increase with increasing basin depth. Parameters that principally measure the duration of body waves were also found to decrease in near-fault areas subject to forward rupture directivity, although such effects were not apparent for other duration parameters that tend to reflect the combined duration of body and surface waves.

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Prediction equations for significant duration of earthquake ground motions considering site and near-source effects - eScholarship

Continuous rigid-frame bridge (CRFB), a type of bridge adopting the unique form of pier-girder consolidation, combines a T-shaped rigid frame with a continuous girder. CRFBs located in western China are likely to suffer destructive earthquakes, which may result in serious damage to bridges. To study the longitudinal seismic responses and damage control of different structure types of the CRFB under strong ground motions, this work develops three nonlinear dynamic analysis models considering the initial internal force state and longitudinal girder-pier pounding effect based on the OpenSEES (version 3.3.0) platform. Moreover, the present study comparatively analyzes the displacement responses, internal force of piers, pounding force and times, and damage condition of the three models and investigates the effectiveness of tuned inerter-based dampers (TIBDs) in controlling seismic responses of the CRFB. The numerical results show that the longitudinal seismic responses of the main piers in the three models are obviously different, especially when subjected to near-fault ground motions. The peak pounding force at the abutments is much larger than at the transition piers, while the pounding times are the opposite. Under near-fault ground motions with a peak ground acceleration (PGA) of 0.4g, the main piers may be damaged moderately or even more seriously, and the bearings are completely destructive. The TIBDs can effectively control the maximum seismic responses and damage degree of the CRFB under pulse-like near-fault ground motions. Among them, both the tuned viscous mass damper and tuned inerter damper are ideal and useful devices. This study can provide useful references for the seismic design and performance analysis of CRFBs. 

Seismic Responses and Damage Control of Long-Span Continuous Rigid-Frame Bridges Considering the Longitudinal Pounding Effect under Strong Ground Motions

Seismic performance improvement of continuous rigid-frame bridges with hybrid control system under near-fault ground motions

Miaoziping Bridge, a long-span rigid-frame bridge, uplift appeared at the end spans in the 2008 Wenchuan earthquake. Bearings and pad stones were damaged during the earthquake. In the past, the uplift mechanism and the seismic response under near-fault and far-fault ground motions were not sufficiently recognized. Here, a refined finite-element model of the Miaoziping Bridge was established considering the initial stress state and the nonlinear characteristics of the girder (e.g., cracking of concrete). The Wenchuan strong motion records and other 40 near-fault pulse-type and 40 far-fault ground motions were selected for nonlinear time history analysis. The uplift effect was realized by considering the compressive-only behavior of bearings. The results show that the seismic responses of the bridge under Wenchuan earthquake ground motions are in good agreement with the real seismic damage observed after the Wenchuan earthquake. The excitation of the near-fault pulse-type ground motion along the longitudinal direction is the dominant factor of the uplift at the end spans. When peak ground acceleration of the near-fault pulse-type ground motion is greater than 0.3g, the end spans are prone to uplift, and the maximum uplift displacement responses can reach 50 cm. There is little uplift possibility subjected to the far-fault ground motions. When the pulse period is in the range of 1–3 s, the pulse effect equals or even exceeds the full-wave effect. The end spans can hardly uplift subjected to vertical or transverse excitation individually. There is a slight difference between the uplift displacements subjected to single longitudinal ground motions and three-directional ground motions. The time of maximum uplift displacement is delayed considering the wave-passage effect. When the wave velocity is less than 1,000 m/s, the adverse effects of the wave-passage effect may be considered. 

Seismic Uplift Effect at End Spans of Long-Span Rigid-Frame Bridges Subjected to Near-Fault and Far-Fault Ground Motions

Continuous rigid-frame bridges (CRFBs) have been widely constructed in high seismicity areas in western China. To investigate the seismic response characteristics and whiplash effect mechanism of CRFBs under near-fault ground motions, a long-span CRFB with high piers is selected as a prototype bridge, and a nonlinear finite element model is developed based on OpenSees. Three groups of near-fault ground motions, namely having forward-directivity pulses, fling-step pulses, and non-pulse, are selected as seismic inputs. These records are intercepted using the significant duration index and scaled to 0.2, 0.4, and 0.64 g, which respectively represent frequent, basic, and rare ground motions. The seismic response characteristics of CRFBs are analyzed and the effects of bearing constraints, ground motion components, and vertical excitation on the seismic responses are discussed. The numerical results show that the longitudinal vibration, transverse whiplash effect, and vertical uplift behavior of the main girder are the main deformation characteristics of CRFBs. Compared with non-pulse earthquakes, the structural displacements, lateral drift angles, bearing deformations, internal forces, and pounding effects are all significantly increased under pulse-like earthquakes. Spatial torsional effects in the mid-span girder and main piers and pounding effects between the girder ends and transition pier top are identified. Perfectly-free and fixed bearings in the transverse direction are not recommended for the seismic design of CRFBs. An optimal stiffness ratio in friction pendulum systems that can minimize the bending degree of the main girder may exist. Furthermore, the uplift of the side-span girder under pure longitudinal excitation is closely related to the pier-girder consolidation form and the rotation of the main piers. The main piers may be tensioned under strong vertical excitation, which is an issue worthy of attention. 

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Seismic response characteristics and whiplash effect mechanism of continuous rigid-frame bridges subjected to near-fault ground motions

To investigate the correlations of duration indexes and the nonlinear seismic responses of long-span continuous rigid-frame bridges with high-rise piers (CRFB-LH), an irregular CRFB-LH was selected...

Correlation Analysis of Ground Motion Duration Indexes and Nonlinear Seismic Responses of a Long-span Continuous Rigid-Frame Bridge with High-Rise Piers

The invention relates to a limiting reinforcement system for a plate-type rubber support bridge. The limiting reinforcement system comprises plate-type rubber supports and a seismic reduction and isolation structure system which is used for limiting excessive sliding of the plate-type rubber support and composed of support limiters. The limiting reinforcement system further comprises piers, a cover beam fixed above the piers, stopping blocks on both sides of the cover beam and a main beam located on the upper end face of the cover beam; the seismic isolation plate-type rubber supports are arranged between the top face of the cover beam and the bottom face of the main beam, the support limiters are mounted at the two ends of each support respectively, the upper and lower support limiters are fixed to the bottom face of the main beam and the top face of the cover beam through bolts respectively, and thin steel plates with polytetrafluoroethylene coatings different in roughness are additionally arranged between the top faces of the plate-type rubber supports and the main beam and between the bottom faces of the plate-type rubber supports and the cover beam to change friction coefficients at both ends of each support; certain gaps are reserved between the upper and lower support limiters and the plate-type rubber supports, and certain gaps are reserved between the upper and lower support limiters. By adopting the structural system, the plate-type rubber supports can be locked under the action of a strong earthquake to avoid excessive sliding.

Limiting reinforcement system for plate-type rubber support bridge

In this study, the uniaxial compressive mechanical properties of earth materials are tested, and the effects of four influencing factors, such as shape, size, curing age, and loading rate, on the strength, damage pattern, and stress-strain curve of the specimens are analyzed. The standard uniaxially compressed specimen size and the recommended loading rate are proposed for the earth specimens. The uniaxial compressive constitutive equations of earth materials are modified on the basis of the Illampas constitutive equation. By fitting the results of this study and typical literature tests, the applicability of the modified constitutive equation form to the uniaxial compressive test curves of soils in different regions of China based on standard sizes is verified. Finally, the formulae for calculating the parameters related to the constitutive equation of earth materials are established. In its application, only the compressive strength of 100-mm-cubic standard specimens with a curing age of 28 d needs to be measured to calculate and determine the specific values of the relevant parameters of the constitutive equation. This is a good reference value for promoting the development of computational analysis methods for earth structures and promoting the engineering design applications of earth structures.

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Fenjie Zhang

Papers

Correlation Analysis of Ground Motion Duration Indexes and Nonlinear Seismic Responses of a Long-span Continuous Rigid-Frame Bridge with High-Rise Piers

Limiting reinforcement system for plate-type rubber support bridge

Study on Mechanical Properties and Constitutive Equation of Earth Materials under Uniaxial Compression