Structural Safety of Prestressed Concrete and Composite Steel Highway Bridges (original) (raw)
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First International Conference on Bridge Maintenance, Safety and Management IABMAS, Barcelona 2002, 2002
Due to the design concept of inclined principal stresses for shear forces applied in the 1960's and 1970's, prefabricated prestressed concrete girders often exhibit insufficient shear resistance according to current standards, since the applied high prestressing ratios allowed reinforcement of the webs with secondary reinforcement only. From the replacement of a 30-year-old road deck, several prefabricated girders became available for full-scale tests. The major results of four-point loading tests and asymmetric three-point loading tests are briefly reported. A step-by-step concept is proposed for the checking of the structural safety of existing concrete structures. This concept also contains refined checks according to the theory of plasticity. Discontinuous stress fields as lower-bound solutions are shown and explained for one of the full-scale tests. Conclusions on checking the structural safety of existing concrete structures are drawn.
Evaluation of . . . Prestressed Concrete Bridges
2007
Within Texas, the procedures in the AASHTO Manual for Condition Evaluation of Bridges (MCEB) are used to determine the load rating of existing structures. A large number of prestressed concrete bridges that were constructed in the 1950s and 1960s have load ratings that fall below the minimum design vehicle specified in the MCEB. The load ratings for this group of are typically controlled by the serviceability limit state criterion related to the tensile stress in the concrete. A low load rating implies that these bridges have experienced damage under service loads. However, observations made by TxDOT personnel during routine inspections indicate that the condition of these bridges is very good, and that there are generally no signs of deterioration. Based on the results of the diagnostic load tests and laboratory fatigue tests, it was concluded that the tensile stress criterion in the MCEB should not be used to evaluate existing prestressed concrete bridges. The calculated tensile s...
IEC2018 Proceedings Book, 2018
Given the vital importance of bridges in life arteries, safety of these structures against destructive agents such as earthquake is of utmost importance. Using pre-stressed columns in bridges will improve their seismic response, because these columns have high displacement capacity during earthquake and a small permanent displacement after earthquake. Therefore, the need for further study on these structures is felt more than ever. In this paper, firstly, prestressed columns were analyzed under reciprocating static load using OpenSees software and results show that pre-stressing bridge columns will improve the quasi-static response of columns and column section bearing. Below, we examine the reliability analysis of pre-stressed bridge samples against force of the earthquake and the effect of different random variables on reliability of bridge. The results show that structural damping and earthquake magnitude have a significant effect on reliability of bridges. Changes in characteristic strength of concrete at ultimate limit and mean resistance of section, effect significantly on reliability of bridge structure.
Revista IBRACON de Estruturas e Materiais
Nowadays it is known that it is important to study the safety of structures to avoid tragic accidents or economic losses. The most widely used method in the world to evaluate the safety of structures is structural reliability. The reliability index of prestressed precast beams of bridges designed using Brazilian standards (NBR6118 and NBR7188) is not known. This work evaluates the annual reliability indexes of a prestressed precast beam bridge at the serviceability limit state (SLS) projected using the Brazilian standard and compares it with results from the literature. The studied bridge has 33.5 meters of span, is simply supported, constituted by five precast concrete beams with U section. The reliability analysis was carried out using two methods for the four limit state equations: First Order Mean Value (FOMV) and First Order Reliability Method (FORM). Sensitivity analyzes were performed to consider both the relative contribution of these variables and the effect of their distri...
Predicted and Measured Performance of Prestressed Concrete Bridges
Journal of Bridge Engineering, 2004
Testing results of six existing prestressed concrete bridges are used to evaluate analytical methodologies. These bridges cover different span lengths, number of lanes, and skew angles. Strains, load distribution factors, and ratings predicted by finite-element analyses and AASHTO code specifications are compared with those from measurements. The comparison reveals a significant difference between the analytical and test results due to the effects of many field factors. Factors that exist in reality but whose effects on bridge performance cannot easily be quantified are defined as field factors. Due to these field factors, existing bridges are different from idealized calculation models and are thus defined as field bridges. To examine this difference and to quantify their effects, some field factors are modeled in a more refined finite-element analysis. It is found that the field factors have a larger effect on the maximum strain than on the load distribution factor. Parametric studies of the effects of diaphragms, bearing stiffness, and skew angles on the load distribution and maximum strain are conducted.
Load and resistance factors for prestressed concrete girder bridges
Budownictwo i Architektura
There has been a considerable progress in the reliability-based code development procedures. The load and resistance factors in the AASHTO bridge design code were determined using the statistical parameters from the 1970's and early 1980’s. Load and resistance factors were determined by first fixing the load factors and then calculating resistance factors. Load factors were selected so that the factored load corresponds to two standard deviations from the mean value and the resistance factors were calculated so that the reliability index is close to the target value. However, from the theoretical point of view, the load and resistance factors are to be determined as coordinates of the so-called “design point” that corresponds to less than two standard deviations from the mean. Therefore, the optimum load and resistance factors are about 10% lower than what is in the AASHTO LRFD Code. The objective of this paper is to revisit the original calibration and recalculate the load and...
Safety Analysis of Prestressed Concrete Bridge beams in Flexure
A probabilistic evaluation of the safety of post-tensioned prestressed concrete simply supported bridge beams at ultimate limit state in flexure as specified in ACI 318 (2002)[1] and EC2 (2008);[2] with due considerations to the loadings recommended in BS 5400 (1978), [3] and AASHTO (2004), [4]; is presented herein and with a review of the relevant design process. Results indicate that the safety of post-tensioned concrete beams is sensitive to the sectional modulus of concrete at the bottom, effective prestress force, profile of eccentricity and the span of the beam in flexure.
Reliability of prestressed concrete girders design: Comparison between NBR and Eurocode codes
This work evaluates the reliability index of prestressed girders beams of highway bridges designed according to Brazilian and European codes concerning the bending ultimate limit state. A model was used to verify the resistant capacity of the beams in the bending ultimate limit state and to evaluate the live load models proposed by the regulations studied. The bridge studied spans 27.4 meters, and four T section prestressed concrete girders support it. To obtain the reliability index , the First Order Reliability Method (FORM) was used, which proved to be very fast and efficient. The values collected by the analytical method are validated using the Monte Carlo simulation method. For all cases, the reliability index value was higher than 5.5, showing that the two normative recommendations for the design of girders beams guarantee a very conservative level of safety.
Structural reliability as applied to highway bridges
Progress in Structural Engineering and Materials, 2000
The paper presents the application of reliability methods in the development of a load and resistance factor design (LRFD) bridge codes. Structural performance is measured in terms of the reliability index. Load and resistance models are summarized. An important step is the selection of the target reliability index and calculation of load and resistance factors. Load and resistance factors are derived so that the reliability of bridges designed using the proposed provisions is at the predefined target level.