Pier Failure Research Articles

Proposed mechanism for mid-span failure of pile supported river bridges during seismic liquefaction

Pile supported river bridge failures are still observed in liquefiable soils after most major earthquakes. One of the recurring observations is the mid span collapse of bridges (due to pier failure) with decks falling into the river while the piers close to the abutment and the abutment itself remain stable. This paper proposes a mechanism of the observed collapse. It has been shown previously through experiments and analytically that the natural period of bridge piers increases as soil liquefies. Due to the natural riverbed profile (i.e. increasingly higher water depth towards the centre of the river), the increase in natural period for the central piers is more as compared to the adjacent ones. Correspondingly, the displacement demand on the central pier also increases as soil progressively liquefies further promoting differential pier-cap displacements. If the pier-cap seating lengths for decks are inadequate, it may cause unseating of the decks leading to collapse. The collapse of Showa Bridge (1964 Niigata earthquake) is considered to demonstrate the mechanism. The study suggests that the bridge foundations need to be stiffened at the middle spans to reduce additional displacement demand.

Evaluation of existing equations for temporal scour depth around circular bridge piers

Scour is defined as the processes of removal of sediment particles from water stream bed by the erosive action of activated water, and also carries sediment away from the hydraulic structures. Scour is the main cause of pier failure. Numerous equations are available for estimating temporal and equilibrium scour depth. The present study describes the phenomenon of temporal scour depth variation at bridge piers and deals with the methods for its estimation. The accuracy of six temporal scour depth equations are also checked in this study. After graphical and statistical analysis, it was found that the relationship proposed by Oliveto and Hager (J Hydraul Eng (ASCE) 128(9):811–520, 2002) predicts temporal scour depth better than other equations. Three equations of equilibrium time of scour are also used for computing equilibrium time. Equilibrium time equation proposed by Choi and Choi (Water Environ J 30(1–2):14–21, 2016) gives better agreements with observed values.

Research on Collapse Process of Cable-Stayed Bridges under Strong Seismic Excitations

In order to present the collapse process and failure mechanism of long-span cable-stayed bridges under strong seismic excitations, a rail-cum-road steel truss cable-stayed bridge was selected as engineering background, the collapse failure numerical model of the cable-stayed bridge was established based on the explicit dynamic finite element method (FEM), and the whole collapse process of the cable-stayed bridge was analyzed and studied with three different seismic waves acted in the horizontal longitudinal direction, respectively. It can be found from the numerical simulation analysis that the whole collapse failure process and failure modes of the cable-stayed bridge under three different seismic waves are similar. Furthermore, the piers and the main pylons are critical components contributing to the collapse of the cable-stayed bridge structure. However, the cables and the main girder are damaged owing to the failure of piers and main pylons during the whole structure collapse process, so the failure of cable and main girder components is not the main reason for the collapse of cable-stayed bridge. The analysis results can provide theoretical basis for collapse resistance design and the determination of critical damage components of long-span highway and railway cable-stayed bridges in the research of seismic vulnerability analysis.

Experimental Investigation of Compressive Behaviour of Pier by Partial Replacement of Metakaolin

Objectives:The main focus of our experimental investigation is to study the behavior of a pier based on variations in compressive strength due to partial replacement of cement with metakaolin in order to attain maximum stiffness and strength, so as to withstand the shear forces, bending moments and other related structural response parameters efficiently. Analysis: The round and rectangular specimens were prepared by replacing cement with metakaolin up to 15%. The samples were tested after 7 and 28 days. Findings: Study reveals that with the replacement of 10% metakaolin in both circular as well as rectangular moulds, there is an increase in the load carrying capacity approximately about 19%, when compared with plain reinforced concrete moulds after 28 days. The most important finding is that the replacement of cement by metakaolin up to 10% helped us to attain higher strength after 7 as well as 28 days hence providing us a simple and efficient method of preventing the pier failure by attaining higher strengths. Improvement/Applications: Based on the test results there is remarkable increase in the load carrying capacity of pier which enhances the rigidity of pier in terms of strength and stiffness.

Evaluation of code criteria for bridges with unequal pier heights

One of the challenges associated with Eurocode 8 and AASHTO-LRFD is predicting the failure of irregular bridges supported by piers of unequal heights. EC8 currently uses “moment demand-to-moment capacity” ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 design procedures for regular seismic behavior, various irregular bridges are simulated through a non-linear pushover analysis using shear-critical fiber-based beam-column elements. The paper investigates the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and proposes different methods for regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all piers irrespective of the different heights and failure mode experienced.

Control of the Local Scouring Around the Cylindrical Bridge Pier Using Armed Soil by Geotextile

Flood currents are considered threatening factors by creating local scour along bridge piers. One method for decreasing local scour is to strengthen the bed against imposed tensions. Among methods which can be appropriate in decreasing and controlling local scour of bridge piers directly is to put riprap beside bridge piers and to employ geotextile around them. Geotextiles form a large group of geosynthetic products produced from polypropylene and polyester fibers, and are used in separation, strengthening and reinforcing, filtration, and drainage. In the present study, the effect of geotextile layer in decreasing local scour of cylindrical single-pier was investigated and the best coverage pattern with the most effect was obtained so that layers with circular and oval shapes were put around the pier relative to its diameter, and the performance of each was compared with the unprotected pier. Test results showed by using geotextile with an appropriate cover, the scour location is transferred to downstream and the scour depth is decreased. These advantages can reduce the risk of pier failure when the duration of flood is short. The results indicate that the scour reduction increases as the layer area increased. In this case the oval layer has a better efficiency compared to the circular one.

Seismic responses of composite bridge piers with CFT columns embedded inside

Shear failure and core concrete crushing at plastic hinge region are the two main failure modes of bridge piers, which can make repair impossible and cause the collapse of bridge. To avoid the two types of failure of pier, a composite pier was proposed, which was formed by embedding high strength concrete filled steel tubular (CFT) column in reinforced concrete (RC) pier. Through cyclic loading tests, the seismic performances of the composite pier were studied. The experimental results show that the CFT column embedded in composite pier can increase the flexural strength, displacement ductility and energy dissipation capacity, and decrease the residual displacement after undergoing large deformation. The analytical analysis is performed to simulate the hysteretic behavior of the composite pier subjected to cyclic loading, and the numerical results agree well with the experimental results. Using the analytical model and time-history analysis method, seismic responses of a continuous girder bridge using composite piers is investigated, and the results show that the bridge using composite piers can resist much stronger earthquake than the bridge using RC piers.

Blast Load Effects on Highway Bridges. II: Failure Modes and Multihazard Correlations

AbstractBridges with different seismic design levels and concrete compressive strengths have been analyzed for three levels of underdeck blast loads. It is observed that there are several other damage modes besides failure of bridge columns that may contribute to a complete collapse of the bridge. In general, it is demonstrated that an increased seismic resistance leads to improved performance during blast loads. Both concrete strength and seismic capacity are equally effective for bridges designed with higher seismic resistance. Extensive simulations have been performed to establish a correlation between the ratio of ductility and strength reduction factor, μ/R, and pier top displacement for concrete with different compressive strengths. It has been observed that the pier top displacement decreases drastically for μ/R>6. Moreover, it is observed from results of 27 simulations that bridge piers with μ/R>6 survive high levels of blast loads (without failure of piers).

Bridge pier failure probabilities under combined hazard effects of scour, truck and earthquake. Part I: occurrence probabilities

In many regions of the world, a bridge will experience multiple extreme hazards during its expected service life. The current American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) specifications are formulated based on failure probabilities, which are fully calibrated for dead load and nonextreme live loads. Design against earthquake loads is established separately. Design against scour effect is also formulated separately by using the concept of capacity reduction (or increased scour depth). Furthermore, scour effect cannot be linked directly to an LRFD limit state equation, because the latter is formulated using force-based analysis. This paper (in two parts) presents a probability-based procedure to estimate the combined hazard effects on bridges due to truck, earthquake and scour, by treating the effect of scour as an equivalent load effect so that it can be included in reliability-based bridge failure calculations. In Part I of this series, the general principle of treating the scour depth as an equivalent load effect is presented. The individual and combined partial failure probabilities due to truck, earthquake and scour effects are described. To explain the method of including non-force-based natural hazards effects, two types of common scour failures are considered. In Part II, the corresponding bridge failure probability, the occurrence of scour as well as simultaneously having both truck load and equivalent scour load are quantitatively discussed.

Bridge pier failure probabilities under combined hazard effects of scour, truck and earthquake. Part II: failure probabilities

Bridge pier failure probabilities under combined hazard effects of scour, truck and earthquake. Part II: failure probabilities

Failure Mechanism Study of Bridge Retainer in Earthquake

Taking a typical continuous girder bridge for example, the text builds spatial beam finite element model. By nonlinear time history analysis method, it analyzes bridge transverse pounding and the retainer strength in different strength levers earthquake. According to bridge pier failure and fragility theory and retainer section moment-curvature analysis, it puts forward retainer failure types in different strength levers earthquake. The calculation results show that it is irrational to design retainer section and reinforcement based on structure requirement. The structural retainer failure types have uncertainty without considering bridge seismic fortification goal. Though it appears on ductility failure, the damage state is very serious.

Simultaneous use of cable and collar to prevent local scouring around bridge pier

Various methods to control scour around bridge piers have been proposed. In the present study the application of cable or collar and a combination of cable and collar were examined experimentally, as countermeasures against local scouring at a smooth circular bridge pier, close to threshold flow conditions of initiation of uniform sediment motion. The results show that the simultaneous use of cable and collar has high efficiency in reducing the scour depth. The best configuration was found for a cable-pier diameter ratio of 0.15 and thread angle of 15°, in which the scour depth in upstream[E1] of the pier reduced to about 53%. In the case of a pier protected with cable and collar the scouring postponed more than pier protected with collar and the rate of scouring is less than in pier protected with collar. These advantages can reduce the risk of pier failure when the duration of flood is short. The results indicate that the scour reduction increases as the cable diameter increased and the thread angle decreased.

The Comparison of Two Methods on the Reliability of Ship Collision for Bridge Based on Applied Mechanics

As for the reliability of ship-bridge collision, function relation between the structure response variable and basic variable is very complex and the traditional theory has been difficult to work it out, so we need the help of finite element numerical method to obtain the solution. APDL language and two methods are used to solve the reliability of ship-bridge collision, compared to seven MCS method conditions and ODRSM-MCS probability of failure of bridge pier. The pier failure probability of 10000 MCS method sampling and ODRSM-MCS sample is very close. ODRSM-MCS method and the MCS method to the case of the same accuracy, while MCS reliability is used in the calculation, the time used is 280min and the ODRSM-MCS mix of computational time is 5min. So the ODRSM-MCS method is much more efficient and effective.

지반 비선형성을 고려한 다경간 연속교의 지진취약도

Seismic performances of existing structures should be assessed with more accuracy for cost-effective retrofits. Existing bridges are assessed by the current guidelines in which a simple method has been adapted considering the technical level of engineers of the historical time of construction. Recently many probabilistic approaches have been performed to reflect the uncertainties of seismic input motions. Structures are modeled frequently with the neglection of soil foundations or modeled occasionally with elastic soil spring elements to consider the effect of the soil on the structural response. However, soil also shows nonlinearity under seismic events, so this characteristic should be reflected in order to obtain a more accurate assessment. In this study, a 6-span continuous bridge has been analyzed under various seismic events, in which the soil was represented by equivalent linear spring elements having different properties according to the intensities of the input motions experienced. The seismic vulnerabilities with respect to the failure of piers and the dropping of the super-structure were evaluated on the basis of the analysis results.

The role of soil in the collapse of 18 piers of Hanshin Expressway in the Kobe earthquake

An investigation is presented of the collapse of a 630 m segment (Fukae section) of the elevated Hanshin Expressway during the 1995 Kobe earthquake. The earthquake has, from a geotechnical viewpoint, been associated with extensive liquefactions, lateral soil spreading, and damage to waterfront structures. Evidence is presented that soil–structure interaction (SSI) in non-liquefied ground played a detrimental role in the seismic performance of this major structure. The bridge consisted of single circular concrete piers monolithically connected to a concrete deck, founded on groups of 17 piles in layers of loose to dense sands and moderate to stiff clays. There were 18 spans in total, all of which suffered a spectacular pier failure and transverse overturning. Several factors associated with poor structural design have already been identified. The scope of this work is to extend the previous studies by investigating the role of soil in the collapse. The following issues are examined: (1) seismological and geotechnical information pertaining to the site; (2) free-field soil response; (3) response of foundation-superstructure system; (4) evaluation of results against earlier studies that did not consider SSI. Results indicate that the role of soil in the collapse was multiple: First, it modified the bedrock motion so that the frequency content of the resulting surface motion became disadvantageous for the particular structure. Second, the compliance of soil and foundation altered the vibrational characteristics of the bridge and moved it to a region of stronger response. Third, the compliance of the foundation increased the participation of the fundamental mode of the structure, inducing stronger response. It is shown that the increase in inelastic seismic demand in the piers may have exceeded 100% in comparison with piers fixed at the base. These conclusions contradict a widespread view of an always-beneficial role of seismic SSI. Copyright © 2005 John Wiley & Sons, Ltd.

Up-Down Vibration Effects on Bridge Piers

A relatively large up-down vibration was recorded during the 1995 Hyogoken-Nanbu earthquake. Many people in Kobe area felt a strong up-down shock at the beginning of the earthquake. The effect of this vibration is not normally considered in the seismic design of bridge piers. Many different types of failure and damage of bridge piers were observed after the earthquake. Most of the concrete piers were damaged by bending or shear, or a combination of the two forces.Some damages in a pier such as a racket type, however, seem to be affected by uniaxial tension. Seismic analysis of bridge piers was performed to check the effect of up-down vibration. Evaluation of up-down impact effect on bridge piers and chimneys was also attempeted. The time dependent dynamic analysis represented the shear or bending failure of the piers and the analysis confirmed that the up-down vibration recorded during the earthquake only had a minor effect on the failure.Analysis of piers due to up-down impact load indicated the possibility that concrete bridge piers might be affected by the uniaxial tension which was imposed at the beginning of the earthquake. A strange failure associated with horizontal cracking which occurred near the top of bridge columns might have been affected by the up-down impact.

Floods and Landslides in Natal and Notably the Greater Durban Region, September 1987: a Retrospective View

The low-lying and coastal areas of Natal, South Africa, were subjected to severe flooding in September 1987. This followed exceptionally heavy rainfall which in four days exceeded 600 mm. The resultant floods were the worst in South African history. Saturation of soils occurring on slopes gave rise to landslides, particularly mudflows. The floods and landslides caused damage estimated at over 600 million rands, and 380 lives were lost. The river gradients in Natal are steep and flow velocities of up to 7 m/sec occurred under these flood conditions, leading to rapid runoff and discharge of large volumes of water which caused severe erosion. The type and extent of erosion in estuaries of large rivers was governed by the type of sediments present in banks and beds, and rock outcrops. Gravel and sand were removed from the beds of large estuaries in preference to the cohesive materials of the banks. General scour depths at times exceeded 10 m, but around bridges total scour below the original river bed may have exceeded 20 m. This, as well as pressure from accumulating debris, caused the displacement of founding caissons of bridges and subsequent pier failure. Furthermore, approach roads to bridges suffered severe erosion. However, none of the newer bridges which were designed in accordance with modern flood magnitude prediction failed. In rural areas, river crossings, mostly fill-over culvert and drift type structures, failed primarily through erosion and overtopping. The heavy rainfall helped trigger a large number of landslides causing damage to property, particularly in the greater Durban area. The most notable slides occurred as mudflows in areas underlain by sandstones, which had been previously considered stable. These localities had thin soil cover which became saturated quickly. In other areas translational and rotational slides occurred, such as in soils overlying granite-gneiss. In rural areas slides were responsible for damage to informal developments on steep slopes. Sliding also occurred in soils above shales, and in recently weathered dune sand.