Load And Resistance Factor Design Research Articles

Live Load Distribution Factors for Skew Stringer Bridges with High-Performance-Steel Girders under Truck Loads

Because the methods used to compute the live load distribution for moment and shear force in modern highway bridges subjected to vehicle loading are generally constrained by their range of applicability, refined analysis methods are necessary when this range is exceeded or new materials are used. This study developed a simplified method to calculate the live load distribution factors for skewed composite slab-on-girder bridges with high-performance-steel (HPS) girders whose parameters exceed the range of applicability defined by the American Association of State Highway and Transportation Officials (AASHTO)’s Load and Resistance Factor Design (LRFD) specifications. Bridge databases containing information on actual bridges and prototype bridges constructed from three different types of steel and structural parameters that exceeded the range of applicability were developed and the bridge modeling verified using results reported for field tests of actual bridges. The resulting simplified equations for the live load distribution factors of shear force and bending moment were based on a rigorous statistical analysis of the data. The proposed equations provided comparable results to those obtained using finite element analysis, giving bridge engineers greater flexibility when designing bridges with structural parameters that are outside the range of applicability defined by AASHTO in terms of span length, skewness, and bridge width.

Towards a Reliability-Based Pavement Design using Response Surface Methods

Reliability has been incorporated in many pavement design procedures to account for the effects of inputs variabilities and uncertainties on predicted performance. The American Association of State Highway and Transportation Officials (AASHTO) mechanistic empirical pavement design guide (MEPDG) computes the reliability of pavement sections with the assumption that the variability of predicted distresses follows normal distribution. This approach does not account for the systematic contribution of each design input variability on the overall output variance. This paper evaluates a two-component reliability analysis methodology for pavement application. The two-component reliability analysis methodology uses a response surface method (RSM) for a surrogate model generation and the first order reliability method (FORM) for reliability computation. Three different response surface methods (central composite, Box–Behnken and Doehlert designs) were implemented and statistically verified for their suitability for surrogate model generation. The two-component reliability analysis methodology was further utilized for the generation of partial safety factors for the development of a load and resistance factor design (LRFD) procedure for pavement applications. Field pavement sections with a wide range in design inputs and target reliabilities were used to evaluate the proposed reliability analysis methodology. The results have shown that the three RSM can be used effectively for pavement reliability problems.

FAST-PACED CONSTRUCTION OF THE NEW KHALIFA PORT BRIDGE PROJECT

The significant growth and development in the United Arab Emirates in recent years necessitated considering advanced construction techniques for bridge structures. This paper presents features of the New Khalifa Port Project which consisted of bridge structures with a combined length of 3.64 km. The strict project design criteria, schedule and budget represented significant challenges which required considering specific designs using efficient precast elements and construction methods. The bridge structural system consisted of 39.8 m long precast, pretensioned modified AASHTO (American Association of State Highway and Transportation Officials) girders with cast-in-place concrete deck slabs. The main challenge was to optimize the size of the precast girder as the self-weight of the initially proposed elements exceeded the lifting capacity of the available equipment. The other challenge was to correlate between the British Standards and AASHTO LRFD (load and resistance factor design) code to design the girders for static and dynamic loads. The casting yard was set at 70 km from the project site and delivery roads were assigned to accommodate the special tandems carrying girders weighing 80 tons each. Lessons learned during design, fabrication, transportation and construction of the precast girders add on to the efficiency of the Accelerated Bridge Construction (ABC) processes.

A new live load model for bridges carrying light rail transit

This paper presents the development of a standard live load model for light rail bridges. It is recognized that the absence of a standard load model causes design outcomes varying from agency to agency, which is problematic from performance and reliability standpoints. A blend of deterministic and probabilistic approaches is employed to propose a new load model. Pursuant to light rail transit guidelines, benchmark bridges are designed (steel plate, prestressed concrete multicell box, reinforced concrete tee-beam, prestressed concrete I and bulb-tee, and steel box girder bridges). Finite element analysis is conducted to examine the response of the bridges when loaded by representative light rail trains operated in the United States (Colorado, Massachusetts, Minnesota, and Utah). Parametric investigations in conjunction with numerous loading configurations (48,256 model cases) characterize light rail train loadings, and corresponding results are exploited to determine the extreme bending moments and shear forces of the bridges at four probability levels (the average, upper 20%, 99.9%, and 75-year categories). The upper 20% model shows load effects similar to the standard live load model (HL-93) of the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications (BDS). The 99.9% and 75-year models envelop the moments and shear forces resulting from the representative light rail trains. These candidate load models are further assessed against site-based load inference. The 75-year model is selected and proposed to be the standard live load model entitled LRT-16 (a uniformly distributed load of 14 kN/m plus three axles of 150 kN at a spacing of 4.3 m, which is configured similarly to those of HL-93 in AASHTO LRFD BDS). The applicability of the standard load model is evaluated using 33 light rail tra.

Analisis Kekuatan Jembatan Konstruksi Baja Sungai Merangin Teluk Wang

Merangin Regency has many natural beauty and has various tourist attractions. One of them is Wang waterfall which is located in Biuku Tanjung village. To get to the object, once visitors must cross the river by boat. But now the government has built a pedestrian bridge with a span 48 meters to the waterfall tourist attractions, making it easier for visitors. Every year the visitors are growing. The purpose of this study is to analyze the strength of the bridge that is in the tourist attraction. Load and Resistance Factor Design (LRFD) method used in analyzing bridges with 2 dimensional structure modeling in the form of portal structure. The data in this research is primary data obtained with direct observation and measurement of field and secondary data is drwing plan of bridge. From the results of structural calculation analysis, all of the planned dimensions meet the strength and security requirements of the structure.Key words : Steel Structure, pedestrian bridge, LRFD method

System Reliabilities of Planar Gravity Steel Frames Designed by the Inelastic Method in AISC 360-10

AbstractCurrent methods for designing steel structures, such as load and resistance factor design (LRFD) are based on safety checks of individual members derived from elastic analysis. The next gen...

Reliability-based design of tunnelling problems and insights for Eurocode 7

The partial factor design approach has been suggested to replace the factor of safety design in geotechnical practice, such as the Eurocode 7 (EC7) for European countries and the load and resistance factor design (LRFD) for the North America. However, these design codes cover little about rock engineering principles and rock engineers struggle with the application of the partial factor design to rock engineering problems. This paper presents how reliability-based design (RBD) can provide insights to and help the evolution of the partial factor design approach for tunnelling problems. Compared with other reliability methods, the first-order reliability method (FORM) is consistent for different but mathematically equivalent limit state functions. The intuitive expanding ellipsoid perspective and the constrained optimization method for FORM help overcome the conceptual and computational barriers for practitioners. Three case studies are presented to show that RBD via FORM can determine the role (resistance or load factor) of input parameters on a case-by-case basis in ways that prescribed partial factors cannot, including a symmetrical roof wedge above a tunnel, a lined circular tunnel under non-hydrostatic in situ stresses and a circular tunnel reinforced by rockbolts considering multiple failure modes.

Probabilistic Research of Long Composite Cylinders under Uniform External Pressure

This study focuses on the load and resistance factor design (LRFD) procedure for anisotropic long composite cylinders under external pressure. The theoretical analysis is performed, the performance function is presented, the target reliability levels are determined, the statistical characteristics of random variables are researched and the LRFD-based code is calibrated. The results show the LRFD-based design procedure provides explicit and consistent reliability for long composite cylinder, which could lead less conservative design.

Service Limit State Design for Individual Drilled Shafts in Shales

A new service limit state (SLS) design procedure for drilled shafts is described, which utilizes strength resistance factors calibrated to achieve a target probability of failure. The new procedure can be used for varying values of the target probability of failure, and allows the shaft dimensions, soil strength, variability of soil strength, loads, and allowable settlement to be adjusted freely in the design. The procedure eliminates the need to establish resistance factors for the SLS on a case-by-case basis, which is a current practical issue for load and resistance factor design (LRFD). Sensitivity analyses presented indicate that resistance factors for a broad set of SLS design conditions can be reasonably established considering four parameters: the target probability of failure, normalized load, normalized shaft dimension, and the variability of soil/rock strength. Calibrated resistance factors are presented as a function of these four parameters in the form of resistance factor charts, as well as in the form of analytical equations developed through regression of the rigorously calibrated resistance factors. The proposed resistance factors range from 0.1 to 0.4, primarily because of the significant variability and uncertainty associated with side resistance for drilled shafts in shale.

Flexural distortional strength of steel beams determined by finite-element modelling

This paper reports on the development of a three-dimensional finite-element model for inelastic non-linear flexural buckling analysis of steel I-beams. The model was used to investigate the effects of unbraced length and yield strength on member moment capacity. Unlike existing design codes, the model considers the effect of web distortions in a lateral-distortional buckling mode. Beam slenderness ranges can be divided into three main regions depending on the failure type – low slenderness (plastic), intermediate slenderness (inelastic buckling) and high slenderness (elastic buckling). Structural design codes give criteria that specify some form of transition from the end of the elastic region to the plastic moment. In the work reported in this paper, the effect of yield strength and web distortion on the limiting laterally unbraced length for the limit state of inelastic lateral-torsional buckling (LTB) was investigated. The numerical beam strengths were compared with the design strengths predicted by current design codes, specifically the load and resistance factor design (LRFD) of the American Institute of Steel Construction (AISC), Australian Standard AS 4100 and BS EN 1993-1-2.

00.01: Future challenges and developments in the design of steel structures – an Australian perspective

ABSTRACTThe paper provides an overview of recent advances towards developing the Direct Design Method (DDM) and its implementation in design standards. The DDM allows design by advanced structural analysis (GMNIA) requiring no recourse to a design standard for checking member or cross‐sectional strength. As the capability of structural analysis programs increasingly incorporate both geometric and material nonlinear effects, and as standard desktop computers have become sufficiently powerful to run GMNIA analysis, the DDM is poised to become the future method of design. The paper outlines the system reliability framework that underpins the DDM and the calibration of the Method for 2D and 3D hot‐rolled structural frames as well cold‐formed structural frames featuring cross‐sectional instability. The system reliability implications of the DDM and load and resistance factor design (LRFD) are discussed. The paper also discusses the philosophy of teaching steel structural design and argues this is most rationally and efficiently undertaken using the DDM. Lastly, the paper comments on ongoing and future developments on the DDM including the implementation of the method in design practice.

13.11: DSM design approach for hot‐rolled steel angle columns

ABSTRACTThis work reports the latest results of an ongoing investigation on the Direct Strength Method (DSM) design of hot‐rolled steel equal‐leg angle columns with fixed and pinned (cylindrical or spherical hinges) supports and short‐to‐intermediate lengths, i.e., buckling in flexural‐torsional modes. It extends the scope of similar studies carried out by the authors for cold‐formed (higher leg width‐to‐thickness ratios) steel angles with the same characteristics. After reviewing (i) the most relevant findings unveiled in the studies concerning hot‐rolled steel angles, including the role played by residual stresses in eroding their ultimate strength, and (ii) the available experimental and numerical failure load data, comprising fixed‐ended and pin‐ended columns with several geometries (cross‐section dimensions and length) and reported by various researchers, the paper briefly addresses the mechanical reasoning behind an efficient DSM‐based design approach proposed by the authors in the context of cold‐formed steel (slender legs) short‐to‐intermediate angle columns. Then, the available failure load data is used to assess the quality of their estimates provided by this DSM design approach, including the determination of the corresponding Load and Resistance Factor Design (LRFD) resistance factors. It is shown that the proposed design approach can be also successfully applied to predict hot‐rolled steel angle column failure loads, leading to LRFD resistance factors above the value currently prescribed, for compression member design, by the North American Specification (ϕc=0.85).

LRFD guides for driven piles considering pile set-up phenomenon

By using an electronic database consisting of previously tested pile data and ten completed full-scale pile tests in Iowa, USA, load and resistance factor design (LRFD) resistance factors considering various construction control methods and set-ups were developed. The focus of this paper is on technology transfer from research to practice as the resistance factors derived at the end of the research required modifications. In a collaboration between a state agency, a private company and a university, this effort facilitated the development of a pragmatic LRFD design guide considering the pile set-up phenomenon that is suitable for use by design engineers. A summary of the joint effort and details of the end product as a lesson for other transportation agencies and similar future endeavours is presented in this paper, which highlights the steps beyond research needed to make the research outcomes valuable for practical use in design and construction while promoting the use of the LRFD principle for pile design.

LRFD Calibration of Simple Soil-Structure Limit States Considering Method Bias and Design Parameter Variability

A general closed-form solution for the reliability index (or probability of failure) of a simple linear limit-state design function with one load term and one resistance term is used to compute the resistance factor expressed in a load and resistance factor design (LRFD) format. The solution considers method bias, bias dependencies, and uncertainties in choice of nominal values of load and resistance determined as part of the project-specific design process. Uncertainty in the choice of nominal values for design is linked quantitatively to the concept of project level of understanding that has been recently adopted in Canadian design practice. All random variables are assumed to be lognormally distributed. Parametric analyses are carried out to show that ignoring possible correlations between random variables can lead to conservative (safe) values of resistance factor and in other cases to nonconservative (unsafe) values. Example LRFD calibrations are carried out using different load and resistance models for the pullout internal stability limit state of steel-reinforced soil walls together with matching bias data reported in the literature. The results demonstrate the practical influence of model type, method bias statistics including dependencies, and operational factor of safety on computed resistance factors.

A novel reliability technique for implementation of Performance-Based Seismic Design of structures

A unified Performance-Based Seismic Design (PBSD) procedure is proposed and successfully implemented. It provides an alternative to the currently used life safety design requirement. To successfully develop the concept, structures are represented by finite elements and excited by the seismic loading in time domain. A novel reliability evaluation procedure is proposed for such representation. An improved response surface based procedure is proposed by combining it with the First-Order Reliability Method (FORM) and the appropriate response surfaces are constructed by combining the saturated design and the central composite design sampling schemes. Performances are defined in terms of Collapse Prevention (CP), Life Safety (LS), and Immediate Occupancy (IO), as commonly used in the profession. The corresponding risks are evaluated by exciting a 9-story steel frame designed by experts satisfying all post-Northridge seismic design requirements. It was excited by 20 earthquake time histories for each performance level and the corresponding probabilities of failure were estimated. It took around 300 deterministic evaluations. The accuracy of the method was established using 600,000 cycles of Monte Carlo simulations. The probabilities of failure estimated using the proposed algorithm are very similar to that of simulations indicating that it is accurate. The probability of failure for two serviceability limit states (overall and inter-story drifts) are very similar, indicating that the procedure will satisfy the basic intent of PBSD. They are also similar to the values used in developing the Load and Resistance Factor Design (LRFD) guidelines used in many current design codes. Designing a structure using multiple time histories, as suggested in recent design guidelines, is a step in the right direction. From the results and the observations made in this study, the authors believe that they proposed a robust, efficient, and accurate unified PBSD procedure and documented its implementation potential.

Big Data for condition evaluation of constructed bridges

This paper presents Big Data analytics on the condition evaluation of highway bridges in the United States. A large dataset comprising 1,002,172 bridge decks and superstructures is constructed, based on the National Bridge Inventory (NBI), and categorized into four service zones as specified in the American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications. The condition rating of the bridge members is examined statistically and probabilistically, in conjunction with the effect of traffic and environment (i.e., temperature and precipitation). The statistical characterization of the members indicates that concrete-based superstructures are predominant in Zones 1, 2, and 3 (79%, 72%, 85%, respectively), whereas steel- and timber-based superstructures account for 51% and 21% in Zone 4, respectively. The bridges in Zones 1 and 3 are subjected to significantly high traffic-induced loading relative to those in Zones 2 and 4. Thermal loading is noticeable in Zones 1 and 4. The deterioration of bridge decks rapidly develops at the bridges’ early service life, and stabilizes with time owing to maintenance and repair efforts. According to a two-factor analysis of variance, adequate selection of structural types dependent upon service environments enhances the performance and longevity of constructed bridges. The likelihood of deterioration of bridges constructed in Zones 1 and 3 is higher than that of the bridges in Zones 2 and 4.

Robust LRFD Resistance Factor Calibration for Axially Loaded Drilled Shafts in Las Vegas

AbstractResistance factors for load and resistance factor design (LRFD) of axially loaded drilled shafts in the Las Vegas Valley are calibrated using data from 41 field load tests. In addition to t...

Effect of pavement maintenance cycle on the fatigue reliability of simply-supported steel I-girder bridges under dynamic vehicle loading

In this study, the effect of the pavement maintenance cycle on the fatigue reliability of simply-supported steel I-girder bridges under dynamic vehicle loading is studied. The bridge model and the fatigue load model are both adopted from the Load and Resistance Factor Design (LRFD) Bridge Design Specifications of the American Association of State Highways and Transportation Officials (AASHTO). A three-dimensional vehicle-bridge coupled model is developed to simulate the vehicle-bridge interaction and used to obtain the stress ranges of the steel bridge girders under the dynamic vehicle loading. Numerical simulations are carried out to study the influence of three important parameters, including the road surface condition, bridge span length and vehicle speed, on the fatigue damage induced by the fatigue truck. The results from this study show that the bridge fatigue reliability decreases dramatically under repeated dynamic vehicle loads when the road surface condition is very poor and that the pavement maintenance cycle has a significant influence on the bridge fatigue reliability. A procedure for determining the desired pavement maintenance cycle to achieve the target fatigue reliability of steel bridge girders is developed. An example is also provided for demonstrating the proposed procedure.

The monitored and theoretical ultimate moment and ductility of pre‐tensioned HSSCC bridge girders

AbstractSelf‐compacting concrete (SCC) is defined as highly flowable and non‐segregating concrete that does not require mechanical ‐vibration during application. Load testing of bridge girders was investigated on full scale T‐beams of pre‐tensioned high strength self‐compacting concrete (PHSSCC). The girders were monitored by fixing different types of sensors at different locations.The results of ultimate moment are compared to evaluate if such girders can be designed using AASHTO Load and Resistance Factor Design (LRFD) Specifications; AASHTO Standard Specifications for Highway Bridges (STD) and the PCI Bridge Design Manual are intended for structures constructed using conventional (non‐vibrated) concrete. It is concluded that good agreement in results exists for the two methods.Investigations (theoretical and experimental) are needed on the issue of ductility in structural prestressed elements constructed in seismic zones or even, the issue of high strength in SCC. These have also been studied here, with the conclusion that ‐suitable ductility for this type of structure, as would be needed in seismic regions, can be achieved.

Size and Geometry Optimization of Double-Layer Grids Using CBO and ECBO Algorithms

In this paper, the optimum design procedure based on colliding bodies optimization method and its enhanced version are applied to optimal design of two commonly used configurations of double-layer grids, and optimum span–depth ratios are determined. Two ranges of spans as small and large sizes with certain bays of equal lengths in two directions and different types of element groupings are considered for each type of square grids. These algorithms obtain minimum weight grid through appropriate selection of tube sections available in AISC load and resistance factor design (LRFD). Strength constraints of AISC-LRFD specifications and displacement constraints are imposed on these grids. The comparison is aimed at finding the depth at which each of the different configurations shows its advantages. Finally, the effect of support locations on the weight of the double-layer grids is investigated. The results are graphically presented from which the optimum depth can easily be estimated for each type, while the influence of element grouping can also be realized at the same time.