Rehabilitation criteria for post-tensioned voided-slab bridges

2004 ◽  
Vol 31 (6) ◽  
pp. 977-987 ◽  
Author(s):  
C R Scollard ◽  
F M Bartlett
Keyword(s):  
Limit State ◽  
Ultimate Limit State ◽  
Limit States ◽  
Stress Cracking ◽  
Compressive Stresses ◽  
New Construction ◽  
Flexural Resistance ◽  
Ultimate Limit ◽  
Crack Widths ◽  
Post Tensioned

Current rehabilitation practices for aging, post-tensioned, voided-slab bridges typically reduce the geometric properties of the concrete cross section and so permanently increase post-tensioning stresses, change primary and secondary prestress moments, and create new primary and secondary moments because the original concrete restrains shrinkage of the new concrete. These changes affect the resistance of the rehabilitated bridge at limit states specified for new construction in the Canadian Highway Bridge Design Code (CHBDC) and may cause other limit states not currently identified in the CHBDC to govern. Rehabilitation schemes should be checked for a serviceability limit state of tensile stresses due to permanent service loads that exceed the cracking strength of the original concrete, which is typically not detailed to control crack widths. Ultimate limit states to check are (i) flexural resistance over interior supports, where the total factored demand can be increased markedly by the rehabilitation; and (ii) creep-initiated failure of concrete due to permanent compressive stresses. The application of these procedures is illustrated through example calculations for a typical continuous bridge.Key words: post-tensioned concrete, serviceability, ultimate limit state, restrained shrinkage, secondary prestress moments, critical stress, cracking.

Seismic Test Methods for Architectural Glazing Systems

1996 ◽  
Vol 12 (1) ◽  
pp. 129-143 ◽  
Author(s):  
Richard A. Behr ◽  
Abdeldjelil Belarbi
Keyword(s):  
Rational Design ◽  
Limit State ◽  
Test Methods ◽  
Test Method ◽  
Ultimate Limit State ◽  
Limit States ◽  
State Data ◽  
Design Procedures ◽  
Seismic Loadings ◽  
Ultimate Limit

An ongoing effort is being made at the University of Missouri-Rolla to develop standard laboratory test methods and codified design procedures for architectural glass under seismic loadings. Recent laboratory work has yielded some promising results regarding the development of an appropriate seismic test method for architectural glass, as well as identifying ultimate limit states that quantify the seismic performance and damage thresholds of various glass types. Specifically, a straightforward “crescendo-like” in-plane dynamic racking test, performed at a constant frequency, has been employed successfully. Two ultimate limit states for architectural glass have been defined: (1) a lower ultimate limit state corresponding to major glass crack pattern formation; and (2) an upper limit state corresponding to significant glass fallout. Early crescendo tests have yielded distinct and repeatable ultimate limit state data for various storefront glass types tested under dynamic racking motions. Crescendo tests will also be used to identify and quantify serviceability limit states for architectural glass and associated glazing components under dynamic loadings. These limit state data will support the development of rational design procedures for architectural glass under seismic loadings.

An Automated Approach for Designing Monopiles Subjected to Lateral Loads

2017 ◽  
Author(s):  
James P. Doherty ◽  
Barry M. Lehane
Keyword(s):  
Limit State ◽  
Ultimate Limit State ◽  
Lateral Loads ◽  
Limit States ◽  
Laterally Loaded Piles ◽  
Improve Design ◽  
Design Procedures ◽  
Automated Algorithm ◽  
Laterally Loaded ◽  
Ultimate Limit

This paper describes an automated algorithm for determining the length and diameter of monopile foundations subject to lateral loads with the aim of minimising the pile weight, whilst satisfying both ultimate and serviceability limit states. The algorithm works by wrapping an optimisation routine around a finite element p - y model for laterally loaded piles. The objective function is expressed as a function representing the pile volume, while the ultimate limit state and serviceability limit states are expressed as optimisation constraints. The approach was found to be accurate and near instantaneous when compared to manual design procedures and may improve design outcomes and reduce design time and costs.

scholarly journals Secondary Moments due to Prestressing with Different Bond at the Ultimate Limit State

2018 ◽  
Vol 26 (1) ◽  
pp. 10-18
Author(s):  
Jaroslav Halvoník ◽  
Peter Pažma ◽  
Radoslav Vida
Keyword(s):  
Limit State ◽  
Plastic Hinge ◽  
Ultimate Limit State ◽  
Critical Cross Section ◽  
Structural System ◽  
Secondary Effects ◽  
Limit States ◽  
Internal Forces ◽  
Ultimate Limit ◽  
Kinematic Mechanism

Abstract Secondary effects of prestressing develop in statically indeterminate structures (e.g., continuous beams) due to the restraint of deformations imposed by hyperstatic restraints. These effects may significantly influence internal forces and stresses in prestressed structures. Secondary effects are influenced by the redundancy of a structural system, which raises the question of whether they will remain constant after a change in the structural system, e.g., due to the development of plastic hinge(s) in a critical cross-section(s) or after the development of a kinematic mechanism, or if they will disappear when the structure changes into a sequence of simply supported beams. The paper deals with an investigation of the behavior of continuous post-tensioned beams subjected to an ultimate load with significant secondary effects from prestressing. A total of 6 two-span beams prestressed by tendons with different bonds were tested in a laboratory with a load that changed their structural system into a kinematic mechanism. The internal forces and secondary effects of the prestressing were controlled through measurements of the reactions in all the supports. The results revealed that the secondary effects remained as a permanent part of the action on the experimental beams, even after the development of the kinematic mechanism. The results obtained confirmed that secondary effects should be included in all combinations of actions for verifications of ultimate limit states (ULS).

DESIGN OF BOLTED CONNECTIONS SUBJECT TO TORSION AND SHEAR IN THE ULTIMATE LIMIT STRESS STATE

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Mohamed S. Abu-Yosef ◽  
Ezzeldin Y. Sayed-Ahmed ◽  
Emam A. Soliman
Keyword(s):  
Failure Modes ◽  
Focal Point ◽  
Design Method ◽  
Limit State ◽  
Bending Moment ◽  
Steel Structures ◽  
Ultimate Limit State ◽  
Shear Forces ◽  
Limit States ◽  
Ultimate Limit

Steel connections transferring axial and shear forces in addition to bending moment and/or torsional moment are widely used in steel structures. Thus, design of such eccentric connections has become the focal point of any researches. Nonetheless, behavior of eccentric connections subjected to shear forces and torsion in the ultimate limit state is still ambiguous. Most design codes of practice still conservatively use the common elastic analysis for design of the said connections even in the ultimate limit states. Yet, there are some exceptions such as the design method proposed by CAN/CSA-S16-14 which gives tabulated design aid for the ultimate limit state design of these connections based on an empirical equation that is derived for ¾ inch diameter A325 bearing type bolts and A36 steel plates. It was argued that results can also be used with a margin of error for other grade bolts of different sizes and steel of other grades. As such, in this paper, the performance of bolted connection subject to shear and torsion is experimentally investigated. The behavior, failure modes and factors affecting both are scrutinized. Twelve connections subject to shear and torsion with different bolts configurations and diameters are experimentally tested to failure. The accuracy of the currently available design equations proposed is compared to the outcomes of these tests.

Applications of Vector Evaluated Genetic Algorithms (VEGA) in Ultimate Limit State Based Ship Structural Design

2014 ◽  
Author(s):  
Owen Hughes ◽  
Ming Ma ◽  
Jeom Kee Paik
Keyword(s):  
Genetic Algorithms ◽  
Structural Design ◽  
Limit State ◽  
Structural Safety ◽  
Wall Structure ◽  
Ultimate Limit State ◽  
Thin Wall ◽  
Limit States ◽  
Multi Objective ◽  
Ultimate Limit

Ship structural design often deals with multiple objectives such as weight, safety, and cost. These objectives usually conflict with each other, and optimizing a particular solution with respect to a single objective can result in unacceptable results with respect to the other objectives. A reasonable solution to a multi-objective problem is to investigate a set of solutions, each of which satisfies the objectives at an acceptable level without being dominated by any other solution. Genetic algorithms have been demonstrated to be particularly effective to determine excellent solutions to these problems. In this paper a multi-objective GA, called Vector Evaluated Genetic Algorithm (VEGA) is formulated and used to optimize a large and complex thin-wall structure (a complete cargo hold of a 200,000 ton oil tanker) on the basis of weight, safety and cost. The structure weight and cost and all of the stresses are calculated using a realistic finite element model. The structure adequacy is then evaluated using the ALPS/ULSAP computer program (Paik and Thayamballi, 2003) which can efficiently evaluate all six ultimate limit states for stiffened panels and grillages. This example was chosen because the initial design is severely inadequate. The results show that the proposed method can perform ultimate strength based structural optimization with multi-objectives, namely minimization of the structural weight and cost and maximization of structural safety, and also that the method is very robust.

A proposed strategy for seismic design of steel buildings

1999 ◽  
Vol 26 (5) ◽  
pp. 564-571
Author(s):  
DJL Kennedy ◽  
M S Medhekar
Keyword(s):  
Seismic Design ◽  
Limit State ◽  
Evaluation Criteria ◽  
Design Procedure ◽  
Ultimate Limit State ◽  
Seismic Zone ◽  
Steel Buildings ◽  
Limit States ◽  
Design Earthquake ◽  
Ultimate Limit

The conceptual basis of the seismic design procedure in the National Building Code of Canada is reviewed. The design earthquake is specified only for the ultimate limit states at which the performance of both ordinary and important buildings is evaluated by an elastic static analysis in all zones. Criteria for checking the serviceability limit states, which apply to moderate earthquakes that may occur relatively frequently in the life of the building, are not specified explicitly. It is suggested that the current design approach could be improved by adopting a design strategy that addresses as well the serviceability limit states and associated evaluation criteria and gives methods for design and analysis as a function of the seismic zone and the importance of the structure. An earthquake with a return period of 1 in 50 years is proposed tentatively for the serviceability limit states with appropriate drift limits. The proposed serviceability limit states are shown to govern the design of buildings for values of the force modification factor greater, on average, than 3.Key words: analyses, earthquake, seismic design, serviceability limit state, steel, ultimate limit state.

Development of Reliability-Based Criteria for Corrosion Assessment

2018 ◽  
Author(s):  
Riski Adianto ◽  
Maher Nessim ◽  
Dongliang Lu
Keyword(s):  
Failure Probability ◽  
Limit State ◽  
Assessment Criteria ◽  
Ultimate Limit State ◽  
Operating Pressure ◽  
Safety Factors ◽  
Limit States ◽  
Feature Based ◽  
Corrosion Assessment ◽  
Ultimate Limit

Reliability-based corrosion assessment criteria were developed for onshore natural gas and low vapor pressure (LVP) pipelines as part of a joint industry project. The criteria are based on the limit states design (LSD) approach and are designed to achieve consistent safety levels for a broad range of pipeline designs and corrosion conditions. The assessment criteria were developed for two corrosion limit states categories: ultimate limit state, representing large leaks and ruptures; and leakage limit state, representing small leaks. For the ultimate limit state, a safety class system is used to characterize pipelines based on the anticipated severity of failure consequences as determined by pressure, diameter, product, population density and environmental sensitivity. Since the leakage limit state does not result in significant safety or environmental consequences, a single reliability target, applicable for all pipelines at all locations is used. The assessment criteria formulations are characterized by three elements: the equations used to calculate the characteristic demand (i.e. operating pressure) and capacity (i.e. burst pressure resistance at a corrosion feature); the characteristic values of the key input parameters for these formulas (such as diameter, pressure and feature depth); and the safety factors defining the characteristic demand as a ratio of characteristic capacity. The process used to calibrate safety factors and characteristic input parameter values that meet the desired reliability levels is described, and an assessment of the accuracy and consistency of the resulting checks in meeting the reliability targets is included. The assessment criteria include two methods of application: feature-based and section-based. The feature-based method divides the allowable failure probability equally between all features. It is simple to use, but conservative in nature. It is suitable for pipelines with a small number of corrosion features. The section-based method considers the failure probability of the corrosion features in a pipeline section as a group, and ensures that the total group failure probability is below the allowable threshold for the section. This method produces less conservative results than the feature-based method, but it requires more detailed calculations. It is suitable for all pipelines, and is particularly useful for those with a large number of features. The practical implications of the application of these criteria are described in the companion paper IPC2018-78608 Implementation of Reliability-based Criteria for Corrosion Assessment.

Stresses In Tendons Of Post-Tensioned Concrete Structures At Ultimate Limit State

2020 ◽  
pp. 10-16
Keyword(s):  
Limit State ◽  
Concrete Structures ◽  
Ultimate Limit State ◽  
Design Code ◽  
Unbonded Tendons ◽  
Current Design ◽  
Ultimate Moment ◽  
Experimental And Theoretical Studies ◽  
Ultimate Limit ◽  
Post Tensioned

Currently post-tensioned concrete structures, which are designed with bonded or unbonded tendons, are widely used in construction. The features of calculation of post-tensioned structures with unbonded tendons, which are contained in some other design codes, are considered. It is noted that the current design code for plain and reinforced concrete structures include the provisions for the calculation of post-tensioned concrete structures with bonded tendons. However, there are no recommendations for the calculation of post-tensioned concrete structures with unbonded tendons, taking into account the specific features of the stress-strain state of structures with such prestressing tendons. These features significantly affect both the ultimate moment resistance of structures and their deformations, usually in the unfavorable direction in comparison with structures in which the bonded tendons are accepted. Therefore, the main attention when developing a method for calculating of post-tensioned concrete structures with unbonded tendons was paid to determining the stresses in such reinforcement at the ultimate limit state capacity check. As a result, a method for determining the stresses and increase of the stress from the external load in the unbonded tendons was developed for calculating the ultimate moment resistance of structures. The proposed method presented in the article showed a close correspondence with the data obtained from other studies, in which the stresses in the unbonded tendons were determined by the results of experimental and theoretical studies.

Observed Performance of Residential Masonry Veneer Construction in the 2010/2011 Canterbury Earthquake Sequence

2013 ◽  
Vol 29 (4) ◽  
pp. 1255-1274 ◽  
Author(s):  
Dmytro Dizhur ◽  
Lisa Moon ◽  
Jason Ingham
Keyword(s):  
New Zealand ◽  
Limit State ◽  
Ultimate Limit State ◽  
Earthquake Performance ◽  
Canterbury Earthquake Sequence ◽  
Continued Use ◽  
Damage Type ◽  
Ultimate Limit ◽  
Crack Widths ◽  
Different Levels

Following the 2010/2011 Canterbury, New Zealand earthquakes, a detailed door-to-door survey was conducted in the Christchurch region to establish the earthquake performance of lightweight timber-framed residential dwellings with a masonry veneer external cladding system. The post-earthquake survey involved documenting the condition of dwellings in areas that had experienced different levels of earthquake shaking, allowing comparison between the performance of different veneer systems and different shaking intensities. In total, just fewer than 1,100 residential dwellings were inspected throughout the wider Christchurch area. The survey included parameters such as level of veneer damage, type of veneer damage, observed crack widths, and level of repair required. It is concluded that based on observed earthquake performance at the shaking intensities matching or exceeding ultimate limit state loading, the post-1996 veneer fixing details performed satisfactorily and continued use of the detail is recommended without further modification.

scholarly journals Probabilistic Approach to Limit States of a Steel Dome

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5528
Author(s):  
Paweł Zabojszcza ◽  
Urszula Radoń ◽  
Waldemar Szaniec
Keyword(s):  
Normal Distribution ◽  
Limit State ◽  
Probabilistic Approach ◽  
Random Variables ◽  
Structural Safety ◽  
Ultimate Limit State ◽  
Limit States ◽  
Serviceability Limit State ◽  
First Case ◽  
Ultimate Limit

In this paper, Numpress Explore software, developed at the Institute of Fundamental Technological Research of the Polish Academy of Sciences (IPPT PAN), was used to conduct reliability analyses. For static-strength calculations, the MES3D module, designed by the authors, was employed. Ultimate limit state was defined as condition of non-exceedance of the capacity value, resulting from the stability criterion of the bent and compressed element. The serviceability limit state was defined as the condition of non-exceedance of allowable vertical displacement. The above conditions constitute implicit forms of random variable functions; therefore, it was necessary to build an interface between the Numpress Explore and MES3D programs. In the study, a comparative analysis of two cases was carried out. As regards the first case, all adopted random variables had a normal distribution. The second case involved a more accurate description of the quantities mentioned. A normal distribution can be adopted for the description of, e.g., the randomness in the location of the structure nodes, and also the randomness of the multiplier of permanent loads. In actual systems, the distribution of certain loads deviates substantially from the Gaussian distribution. Consequently, adopting the assumption that the loads have a normal distribution can lead to gross errors in the assessment of structural safety. The distribution of loads resulting from atmospheric conditions is decidedly non-Gaussian in character. The Gumbel distribution was used in this study to describe snow and wind loads. The modulus of elasticity and cross-sectional area were described by means of a log-normal distribution. The adopted random variables were independent. Additionally, based on an analysis of the elasticity index, the random variables most affect the failure probability in the ultimate limit state and serviceability limit state were estimated.

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