Load And Resistance Factor Design Method Research Articles

ASD and LRFD: Reliability comparison for designs subjected to wind loads

Current design practice in the United States allows engineers to use either Allowable Strength Design (ASD) or Load and Resistance Factor Design (LRFD) method, under the assumption that both methods provide similar levels of economy (available design strengths) and safety (probabilities of failure and reliability indices) regardless of the design conditions. Recent studies have demonstrated that significant differences in economy can arise between ASD- and LRFD-based designs subjected to combinations of gravity and wind loads, suggesting inconsistencies between the safety levels. This study investigates the safety levels provided by the ASD and LRFD methods for such design cases. The safety levels were estimated using a formal reliability analysis with consideration of geometrically non-linear second-order effects. The reliability analysis was performed using Monte Carlo simulations with appropriate probability distributions for the random variables associated with both resistance and loads. The findings of this study indicate that generally accepted uniformity of reliabilities achieved by the ASD and LRFD methods does not hold for design cases governed by wind loads. The safety levels achieved by using the ASD method are less consistent than those achieved by using the LRFD method. The use of the ASD method generally entails the acceptance of failure risks many times greater than for those of the LRFD method, and target safety levels lower than those stipulated by the ASCE 7 Standard. These results highlight the need for a reevaluation of the current design practices to ensure that the required target levels of structural safety are consistently met.

Unified Flexural Resistance Design Method and Evaluation Frame for the B-Regions of RC Flexural Members—Theory and Application

The load and resistance factor design (LRFD) method is normally used to design B-regions of reinforced concrete (RC) flexural members. The design includes many checks corresponding to different limit states. The LRFD method requires many loop calculation steps in the design, demonstrating its relative inefficiency. It cannot be applied to compare limit states directly and quantitatively. Different design limit states are separated and isolated. How to improve the analytical calculation efficiency of the LRFD method and to realize direct and quantitative comparisons between limit states are very important problems in structural engineering. This paper presents an innovative unified flexural resistance design (UFRD) method and a unified flexural resistance evaluation (UFRE) frame to solve these problems to some extent. The main contents include the unified flexural resistance (UFR) principles, formulas for the unified flexural resistance design (UFRD) method, the operation procedure to facilitate its usage, the UFRE framework to compare limit states, and three examples. The results show that the UFRD method can provide the same design outcomes as the LRFD one. However, UFRD calculations are simpler, requiring at most 20% of the calculation steps of the LRFD method. The UFRE frame can make different limit states compare with each other directly and quantitatively, which cannot be realized by the LRFD method. It helps expose some potential and insufficient flexural resistance hazards for some limit states, such as the only 10% relative strength reservation of one example. Thus, the UFRD method and the UFRE frame supplement and develop the LRFD method to some degree. The simplicity and practicality of the approach and the frame make them appropriate for many applications.

ANALYSIS OF STEEL COLUMN MODELING IN CONSTRUCTION FOR BOILER WAREHOUSE EXPANSION BASED ON SAP SOFTWARE

The superstructure is all components that are above the ground. The function of the superstructure is as a support for the building with an upward elongated shape, such as frames, trusses, beams, and columns. The column is a vertical compression member of the structural frame that carries the load from the beam. The construction of this warehouse is located in Tanjung Morawa using IWF steel columns. In this study, the strength of the steel columns was analyzed by modeling using SAP 2000 V.14 and manually calculated on the F portal using the LRFD (Load and Resistance Factor Design) method. The research method uses primary data, namely direct field observations in the form of interviews, and secondary data, namely data taken from the contractor in the form of pictures or from books, previous research, and so on. Based on the results of structural modeling using SAP 2000 V.14, it was concluded that the building is safe; on manual analysis on the F portal, it can be concluded that the steel columns WF-300×150×9×13 and WF-350×175×7×11 are capable of carrying factored compressive loads.

Kehandalan Struktur Anjungan Lepas Pantai Terpancang Empat Kaki di Perairan Natuna

The design of offshore platforms in Indonesia generally uses Working Stress Design (WSD) method rather than Load and Resistance Factor Design (LRFD) method. Whereas the LRFD method produces designs that better describe real conditions with load and capacity factors. The load and capacity factors are obtained from consideration of the uncertainty or randomness of their values. One of the load factors used is the environmental load factor. The environmental load factor of LRFD method is obtained based on environmental characteristics not in Indonesian waters. There are differences in the environmental characteristics of each water. Uncertainty of environmental loads in the offshore platforms design is wave height, current velocities, and wind speed. To get a structure designed according to the characteristics of the waters in Indonesia, an environmental load factor is needed in accordance with the characteristics of Indonesian water. To achieve that, structural reliability analysis is needed. S tructure s reliabilty represents the possibility of the structure's performance criteria being met which is expressed by the reliability index. The reliability index of structures designed using the WSD method used as a reference for LRFD method. In this study, reliability analysis was carried out using the reserve strength ratio value from the pushover analysis on WSD method. The reliability index of the structure model is 4.10. This value is categorized as high reliability . Th is results can be used as a reference to determine the environmental load factor of Indonesia n water in the future.

Perencanaan Struktur Komposit Baja-Beton Dengan Metode Lrfd (Load And Resistance Factor Design) Ruang Kelas Lantai Iii Smk Pariwisata Labuan Bajo – Flores – Ntt

Planning a steel-concrete composite structure using the LRFD (Load and Resistance Factor Design) method is a method that clearly takes into account the boundary conditions, various load factors, and resistance factors, where in this case the resistance factor is needed to maintain the possible lack of structural strength, while the factor load is used to anticipate the possibility of an overload that is formulated. This planning uses a composite structure that is focused on profile steel beams, steel deck plates, and composite columns. Dead and live loads are calculated based on the Indonesian loading regulations for 1983 buildings, while earthquake loads are calculated based on the earthquake resistance planning procedure for building and non-building structures as stipulated in SNI 1762-2012. The steel-concrete composite structure itself is calculated based on the specifications for the design of steel structure buildings using the LRFD method as stated in SNI 03-1729-2002. The structural analysis in the form of the magnitude of the force acting on the building was carried out using the SAP2000 application while the analysis of the feasibility of using the dimensions of the composite structure based on the SNI used was done manually. From the planning results, the dimensions of beam and column cross-sections for each floor plate 1, 2 and 3 are B1 250/250, B2 250/175, B3 300/150, and K1 350/350. The use of steel decks on floor plates 1, 2, and 3 uses shear connectors (studs) with a diameter of 19 mm with 40, 20, and 25 shear connectors, respectively. The joints used in the main and child beams on floors 1, 2, and 3 respectively use 19 mm diameter bolts with 4 bolts, 2 bolts, and 4 bolts respectively, while the connections to columns and beams use diameter bolts 20 mm with the number of bolts 8 pieces.

A Study on Load-carrying Capacity Design Criteria of Jack-up Rigs under Environmental Loading Conditions

Jack-up drilling rigs are widely used in the offshore oil and gas exploration industry. Although originally designed for use in shallow waters, trends in the energy industry have led to a growing demand for their use in deep sea and harsh environmental conditions. To extend the operating range of jack-up units, their design must be based on reliable analysis while eliminating excessive conservatism. In current industrial practice, jack-up drilling rigs are designed using the working(or allowable) stress design (WSD) method. Recently, classifications have been developed for specific regulations based on the load and resistance factor design (LRFD) method, which emphasises the reliability of the methods. This statistical method utilises the concept of limit state design and uses factored loads and resistance factors to account for uncertainly in the loads and computed strength of the leg components in a jack-up drilling rig. The key differences between the LRFD method and the WSD method must be identified to enable appropriate use of the LRFD method for designing jack-up rigs. Therefore, the aim of this study is to compare and quantitatively investigate the differences between actual jack-up lattice leg structures, which are designed by the WSD and LRFD methods, and subject to different environmental load-to-dead-load ratios, thereby delineating the load-to-capacity ratios of rigs designed using theses methods under these different enviromental conditions. The comparative results are significantly advantageous in the leg design of jack-up rigs, and determine that the jack-up rigs designed using the WSD and LRFD methods with UC values differ by approximately 31 % with respect to the API-RP code basis. It can be observed that the LRFD design method is more advantageous to structure optimization compared to the WSD method.

Reliability-based design of FRP flexural strengthened reinforced concrete beams: Guidelines assessment and calibration

In the past few decades, many guidelines and standards for FRP strengthened reinforced concrete (RC) structures have been presented based on the theory of reliability-based limit state with the load and resistance factor design (LRFD) approach. The LRFD method consists of two formats: the resistance reduction factor format and the material partial safety factor format. In this paper, several well-recognized design guidelines with these two formats for FRP flexural strengthened RC beams have been assessed based on model error and reliability index. First, the model error of each design guideline was evaluated based on a collected test database. Then, the reliability index was obtained by the importance sampling (IS) method, in which the optimum density function is determined by the first-order reliability method (FORM). Finally, the calibration of resistance reduction factor or FRP partial safety factor was performed with different target reliability indexes. The results show that: (1) The model error of each failure mode is different for each design guideline. For flexural failure, China’s GB 50608 2010 has the lowest model error. For intermediate crack-induced (IC) debonding, UK’s TR 55 2012 shows the highest model error. For end debonding, Italy’s CNR-DT 200 R1/2012 is less conservative. (2) It is difficult to meet the pre-given reliability level for some failure modes in several design guidelines using the originally suggested design parameters. For example, GB 50608 2010, fib T5.1 2019 and JSCE 2001. (3) The calibrated resistance reduction factors or the FRP partial safety factors are provided to satisfy the target reliability level. However, it is meaningless and uneconomical to adopt partial safety factors that are too large or reduction factors that are too small to fit into a design. Other options can be chosen such as applying additional anchorages to avoid end debonding, increasing the FRP bonding area, and reducing the FRP thickness to avoid the probability of IC debonding failure.

Reliability-Based Calibration of Resistance Factors in LRFD Method for Driven Pile Foundations on Inshore Regions of Iran

This paper presents the improvement of load and resistance factor design (LRFD) method for axially loaded driven piles in Iran. The LRFD method has been well developed and successfully implemented in geotechnical engineering, especially in the design of pile foundations in different parts of the world. To extend the use of this method in Iran, it is necessary to use the results of reliable local pile load tests and construction records to calibrate LRFD resistance factors regionally. To this end, we first collected a comprehensive database of static and dynamic load tests which have been performed on driven piles in fine-grained soils across Iran. Based on this database, we calculated the resistance factors for different design methods using three different methods of reliability analysis (FORM, FOSM, and MCS) and for two levels of reliability (βT = 2.33 and 3). Finally, we used these calculations together with experience and engineering judgment to propose resistance factors for the National Building Code of Iran.

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

OS0602-279 荷重・強度係数設計(LRFD)のベイズ更新 : 確率有限要素法を援用した形状および荷重条件に変動を伴う構造部材の信頼性設計

This study has applied the Bayesian updating scheme and the stochastic finite element method (SFEM) to the Load and Resistance Factor Design (LRFD) method of a round bar having random geometry. The LRFD method is able to take into account separately the stochastic variability in material strength, in geometrical randomness of structural components and in loads applied to the components. Therefore, this method makes it possible to keep up the reliability of the components during the period of use. The LRFD method, however, has a problem that it requires vast amount of data for performing the design. Addressing this problem, in this study, the Bayesian updating scheme, which requires only small amount of data, has been applied to the LRFD method. The SFEM and the Markov chain Monte Carlo (MCMC) method have been adopted in this study to analyze the stochastic variability in component geometry as well as in loads and to perform the Bayesian updating, respectively in the LRFD.

Effect of Number of Soil Strength Measurements on Reliability of Spread Footing Designs

One of the primary objectives of using load and resistance factor design (LRFD) is to produce designs that consistently reach some established target reliability. Achieving this objective is challenging in geotechnical applications because variability and uncertainty in design input parameters vary substantially from site to site and with different quantities of site characterization. Analyses were performed to simulate spread footing design by using different numbers of undrained shear strength measurements. Results revealed that the likelihood was high of over- or underestimating both the mean value of a design parameter and the uncertainty in the mean value when small numbers of measurements were considered. The analyses also revealed that LRFD methods that prescribed constant resistance factors frequently produced underreliable designs when small numbers of measurements were considered. The percentage of underreliable designs decreased when increasing numbers of measurements were used. However, this decreasing percentage of underreliable designs was accompanied by an increasing percentage of overreliable designs rather than an increasing percentage of designs that achieved the target probability of failure within practical limits. In contrast, LRFD methods prescribing resistance factors that depended on uncertainty in design parameters tended to produce a consistently low percentage of underreliable designs when more than five measurements were used. As greater numbers of measurements were considered, such methods produced increasing percentages of designs that practically achieved the target probability of failure and decreasing percentages of overreliable designs.

Incorporating set-up into LRFD method for drilled shafts

The increase of pile resistance with time is referred to as ‘set-up’. This behaviour of driven piles has been widely discussed in many studies by researchers. Meanwhile, there has been little, if any, information regarding this aspect for drilled shafts. Performing a bearing capacity test for a shaft over time, however, requires higher costs and more complicated rigs compared to a driven pile. A database including results from five Osterberg cell-tested drilled shafts conducted at two different stages is considered, from which the set-up effect is statistically analysed. The reliability-based analysis technique using Monte Carlo simulation (MCS) is used to develop separate resistance factors to account for different degrees of uncertainties associated with the predicted reference resistance and the predicted set-up resistance in the framework of the load and resistance factor design (LRFD) method. By incorporating set-up into design, shaft length or number of shafts can be reduced and economical design of drilled shafts can be achieved.

“DESIGN OF REINFORCED SOIL WALLS BY LRFD APPROACH”

In this paper, the detail of Load and Resistance Factor Design (LRFD) approach which is based on reliability concept for the design of Reinforced Soil (RS) walls is presented. For conventional methods i.e Allowable Stress Design (ASD) Method, the factor of safety is applied only to resistance and loads are considered without variations. For LRFD method, factor of safeties are applied for both load and resistance. Due to availability of large statistical data and economy, this method is preferred. An attempt is made to solve one numerical example of geosynthetic RS walls due to soil selfweight plus permanent uniform surcharge using LRFD as well as other conventional methods (ASD) viz. FHWA, Modified Rankine, NCMA and B.S Code Methods and the results of the LRFD methods are compared with conventional design methods and concluding remarks are presented. The various equations are obtained based on various curves plotted by using ASD and LRFD approaches. From these equations it is clear that if FOS against tensile rupture is known for any RS wall having 7m height and same properties and environmental conditions as mentioned in current study then FOS against pullout failure and pullout capacity can be computed for these walls.

Whatever happened to autostress design?

This paper is a review of the history of inelastic design criteria for steel girder bridges. The AASHTO Specification's evolution from Working Stress Design (WSD) to Load Factor Design (LFD) to Load and Resistance Factor Design (LRFD) will be the connecting thread of the paper. The author has been involved in some way in much of the research that is behind the inelastic design criteria in the AISC and the AASHTO steel specifications. Brief accounts will be given of the theoretical and experimental background for the inelastic provisions in the LFD and LRFD methods for girder bridge design. The background and the implementation of the “Auto-Stress” method will be discussed.

Resistance factors calibration and its application using static load test data for driven steel pipe piles

This paper presents the reliability-based resistance factor calibration of driven steel pipe piles and the implementation of Load and Resistance Factor Design (LRFD) on practical design cases. Resistance factors of driven steel pipe piles were calibrated in the framework based on reliability theory using static pile load test results. The results of fifty seven load tests conducted to failure were compiled and these 57 data were divided into three different groups based on their data quality. For the three groups, reliability analyses were performed for two static bearing capacity equations and for different target reliability indices (2.0 and 2.33 for group piles and 2.5 for single piles) following the First-Order Reliability Method (FORM) and using the Monte Carlo Simulation (MCS). It is noted that the resistance factors were highly dependent on the quality of load test data. To implement the calibrated resistance factors, a case study on an actual bridge foundation design was performed. The case study result showed that, for the given target reliability index, the developed LRFD method using the resistance factors calibrated in this study could contribute to cost savings when it is compared with Allowable Stress Design (ASD) case using a safety factor of 3.0.

Load and Resistance Factor Design (LRFD) of Nuclear Straight Pipes for Loads That Cause Primary Stress

Class 2 and 3 nuclear piping is designed according to the allowable stress design (ASD) method used in the ASME Boiler and Pressure Vessel (B&PV) code, Sec. III, Division 1, NC and ND-3600 according to which safety factors applied to the strength of steel (resistance) provide acceptable safety margins for the piping design. This paper describes the development of design equations according to the load and resistance factor design (LRFD) method for loads that cause primary stress such as sustained weight, internal pressure, and earthquake for different levels of piping operation. The LRFD method differs from the ASD since multiple factors, applied separately to each load and the strength of steel, provide safety margins that correspond to a known and acceptable probability of failure for the piping. Load combinations are provided, statistical properties for the variables under consideration are presented and the partial safety factors are moreover illustrated for different values of the target reliability index.

A Reliability-Based Approach for the Design of Nuclear Piping for Internal Pressure

Nuclear pipes are designed to withstand primary membrane stresses generated by internal pressure according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section III, Parts NB-3641, NC-3641, and ND-3641, which uses the allowable stress design (ASD) method. This paper presents limit states and equations for the design of nuclear pipes for internal pressure based on the load and resistance factor design (LRFD) method. The LRFD method is shown and explained to be more consistent than the ASD method. The paper presents the procedure for the derivation of the partial safety factors. Moreover, these factors are evaluated, example calculations are provided, and comparisons with the present design are made.

The new 2005 AISC specification

In late 2005, the American Institute of Steel Construction issued its most recent Specification for Structural Steel Buildings (ANSI/AISC 360-05). This specification includes updated design provisions in both allowable strength design (ASD) and load and resistance factor design methods (LRFD), and incorporates the design provisions for hollow structural sections and single angles. Amongst the major changes are a complete revamping of the methodologies for assessing stability of framed structures, new provisions for composite columns and updated material requirements. This paper will describe the changes and highlight those of practical significance.

341 荷重耐力設計法を用いた部分安全率の検討(OS10-2 応力拡大係数,確率信頼性,OS10 エネルギー機器の経年変化に関する健全性評価手法の開発とその適用(1))

This paper describes the study on application of partial safety factor for design and maintenance of nuclear power plant facilities. The trend to utilize risk information is activating for the rational design and the maintenance of nuclear power plant facilities. In this study, risk information is assumed as the reliability of components, and the partial safety factor (PSF) for satisfying this requirement was evaluated using Load and Resistance Factor Design method (LRFD). This result suggests that it is possible to rationalize the safety factors defined in conventional Design and Construction Code and Fitness-for-Service Code.

Axial service limit state analysis of drilled shafts using probabilistic approach

Drilled shafts are, typically, designed by considering the axial ultimate limit state. In this design methodology, the axial displacement requirements are verified once the design is completed. As an alternative, drilled shafts may be designed by considering the axial service limit state. Service limit state foundation design is more efficient when done using the load and resistance factor design (LRFD) approach. Furthermore, reliability may be rationally incorporated into the design process that utilizes the LRFD method. In this paper, we develop probabilistic approaches for axial service limit state analysis of drilled shafts. The variability of shaft-soil interface properties is modeled by lognormal probability distribution functions. The probability distributions are combined with a closed-form analytical relationship of axial load-displacement curves for drilled shafts. The closed-form analytical relationship is derived based upon the “t–z” approach. This analytical relationship is used with the Monte Carlo simulation method to obtain probabilistic load-displacement curves, which are analyzed to develop methods for determining the probability of drilled shaft failure at the service limit state. The developed method may be utilized to obtain resistance factors that can be applied to LRFD based service limit state design.