Capacity Reduction Factors Research Articles

Modelling the Entry Capacity Reduction Factor and Pedestrian Movement Analysis at Roundabouts: A Case Study of Tier-II Cities in India

Modelling the Entry Capacity Reduction Factor and Pedestrian Movement Analysis at Roundabouts: A Case Study of Tier-II Cities in India

One-way shear strength design of flat-plate voided slabs

Current design standards do not include design provisions to handle the reduced shear capacity of voided flat-plates, and the current design practice considers its shear capacity as a percentage of the solid slab. The study presents an investigation of the one-way shear capacity of flat-plate voided slabs. The investigation is carried out using a compiled evaluation experimental database and an experimental program. A capacity reduction factor for flat-plate voided slabs, λvoid, is proposed and is a function of void height to the slab height (hvoid/h) ratio. The proposed factor is calibrated to the ACI 318-19 shear model. The proposed factor allows for section optimization based on shear capacity, where the height of the void former can be selected based on the shear load subjected to and the required shear strength. This is not possible using the current practice of the manufacturers, where they use either a constant capacity reduction factor or a factor that is slightly affected by the hvoid/h ratio. The model is applicable for voided slabs with a void former clear spacing of 0.10–0.16 of its diameter, or higher. Incorporating the reduction factor, λvoid, resulted in an average experimental-to-predicted (Vexp/Vpred) of 1.67 and COV of 16 %. By comparing the average Vexp/Vpred and COV of voided slabs to solid slabs, the strength reduction factor (ϕ) of 0.75 for shear will still be applicable.

Numerical studies of pull-through failures in cold-formed steel battens at sub-zero temperatures

Cold-formed steel (CFS) roof and wall cladding systems comprising thin, high strength steel battens and claddings are popularly used in the building industry worldwide. These cladding systems have been observed to encounter failures under combined snow and strong wind actions during blizzards. Significant damage is caused by the disengagement of the entire roof/wall cladding when localised pull-through failures occur in thin-walled steel battens at the batten to truss/rafter screw connections due to a splitting mechanism around the screw head. This study uses detailed finite element analyses of the pull-through failures of a range of batten configurations under combined wind and sub-zero temperature conditions. Suitable finite element models capable of simulating the pull-through failures of battens were developed and validated using experimental results, followed by detailed numerical parametric studies. The main outcomes of this study are accurate design equations and capacity reduction factors essential for predicting the pull-through capacities of CFS battens at sub-zero temperatures.

Impact of urban shielding on radiological risk after a hypothetical nuclear event

Nuclear events have always represented a threat to societies, and nowadays, the concept of tactical nuclear weapons occupies a prominent place in the field of concern. The actual use of such a weapon has not yet been recorded. However, studies involving computationally simulated hypothetical scenarios are periodically published. This study considers a hypothetical event involving the activation of a tactical nuclear device in an urban area. The central objective was to evaluate the protective capacity of urban structures (buildings) for reducing the radiation dose to which the population may be subjected. Analytical computational simulation was applied to create the event. The threshold dose for deterministic effects is the interest isodose for the scenario that considers a 10 kT power device. The concept of Margin of Safety (MoS) was applied to the results in order to turn them into useful information for decision-makers. Applying MoS allowed to organize the urban structures according to their dose reduction capacity (reduction factors). It can be foreseen that in the case of a real application, the proposed methodology will facilitate the classification of structures distributed throughout the urban area, supporting the decision, especially regarding the prioritization of urban zones, and the type of structure. The results showed that it is useful to discriminate urban structures according to criteria conditioned on radiation doses related to deterministic effects. The discrimination introduces scientific basis to advice and support for decision-making, which may increase confidence levels for decision-makers. Therefore a possible positive impact on the optimization of resources and improved conditions for crisis management can be expected.

Effects of In-Plane Damage of infill Walls on Their Out-of-Plane Bearing Capacity Reduction Factors

Effects of In-Plane Damage of infill Walls on Their Out-of-Plane Bearing Capacity Reduction Factors

Pull-out capacities of screw connections in thin steel battens exposed to bushfire conditions

External building envelopes made of cold-formed steel (CFS) claddings are commonly used in bushfire prone areas due to their non-combustible properties. However, their designs should ensure safety under the combined action of enhanced wind suction loading and elevated temperatures experienced during bushfires. Although numerous studies have investigated the critical pull-out failures in CFS batten screw connections under wind suction loading at ambient temperature, the pull-out failure behaviour of batten screw connections under bushfire conditions has not been investigated. The main objective of this study is to examine the pull-out failure mechanisms and capacities of screw connections in CFS battens under wind suction loading at elevated temperatures. Two hundred and sixteen small-scale tests were conducted on CFS battens made of three commonly used thicknesses and both high (G550) and low (G300) strength steels. Tests were conducted at six different temperatures using three types of screw fasteners to investigate the critical localised pull-out failures of batten screw connections. The results of these tests were utilised to develop applicable design equations and capacity reduction factors for the pull-out capacities of batten screw connections under the combined action of wind suction loading and elevated temperatures. The findings of this study will help design and build structures safely in bushfire-prone regions.

Testing and Numerical Simulation of the Shear Resistance of Blind-Bolted Aluminum Connections

Due to their high bending stiffness, high torsional stiffness, and high local stability, rectangular section members of Al alloy space structures are frequently utilized as load-bearing elements. However, the joint construction is more complex because of the closed cross-section. To join rectangular section members without drilling holes in them, a variety of blind bolts that can be placed and fastened on one side have been devised. The blind bolts researched in this paper is known as BOM bolt. The shear resistance of BOM-bolted Al alloy connections is investigated using shear testing and finite element calculations of individual bolts and bolt groups. According to the test and numerical simulation results, the formulas for the compressive strength of the aluminum plate and the shear capacity reduction factor of BOM-bolted long connections are derived.

Durability performance of RC beams strengthened with CFRP laminates and galvanized steel mesh bonded with epoxy and mortar systems

The galvanized steel mesh (GSM) systems are novel strengthening materials for the concrete structural elements, but their mechanical and long-term durability properties are needed to be investigated to enhance understanding and reliability in their use. This study investigates the behavior of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymers (CFRP) and GSM sheets under harsh climatic conditions of saline water and direct sunlight. The main focus was to recommend two important reduction factors, the bond reduction factor and the overall flexural reduction actor, when concrete beams are subjected to two said environments for a long period. These factors were compared to the ones recommended by different codes. The CFRP sheets were attached to the beams’ soffit with epoxy adhesive, whereas the GSM sheets were bonded either with epoxy (SME) or epoxy-based mortar (SMM). The specimens were weathered under saline water and direct sunlight for a period of 6, 12, and 24 months. The load-carrying capacity of CFRP, SMM, and SME strengthened specimens increased by 47%, 55%, and 55%, respectively, when compared to the unstrengthened specimens at 28 days. The bond capacity reduction factors (Rb) for CFRP, SMM, and SME strengthening systems were 0.75, 0.85, and 0.95 for saline water exposure, and 0.95, 0.85, and 0.85 for sun exposure, respectively, over a period of two years. On the other hand, the recommended overall flexure strength reduction factors (Rn) for CFRP, SMM, and SME strengthening systems were 0.85, 0.85, and 0.90 for saline water exposure, and 0.95, 0.90, and 0.90 for sun exposure, respectively. The results suggest that epoxy-based strengthening systems are more durable compared to the mortar-based systems under harsh climatic conditions.

Failure analysis and structural reliability of unreinforced masonry veneer walls: Influence of wall tie corrosion

Corrosion appears to be a very common problem in historical and aged structures with steel ties and anchorages. A potential rapid deterioration of the wall tie due to the corrosion leading to a premature structural failure poses a serious threat to the built heritage infrastructures’ safety. This paper describes an overview of the probabilistic failure analysis of the unreinforced masonry (URM) veneer wall system with flexible backup under uniformly distributed out-of-plane loadings. Moreover, a framework is proposed to consider the wall tie corrosion in the stochastic finite element analysis (FEA) while estimating the structural reliability. A probabilistic experimental study where 18 full-scale URM veneer wall systems with theoretically identical geometries and properties were tested under inward and outward lateral loading. Wall failure statistics along with the probabilistic characterisation of veneer wall constituent materials including mortar, wall tie and timber were accomplished. A stochastic computational model was then developed which combines the FEA and Monte Carlo simulation to evaluate the failure progression and system peak load (veneer capacity) while considering the spatial variability of veneer wall material properties. Two scenarios, with and without wall tie corrosion, are considered, and the probabilistic characterisation of the veneer capacities for these scenarios under inward and outward out-of-plane loading is also reported. The model error statistics were combined with the probabilistic load models to determine the reliability index corresponding to the Australian Standard for Masonry Structures AS 3700. Annual reliabilities are compared to target reliabilities recommended by ISO 2394. Capacity reduction factor and design minimum tie strength consideration for corroded wall tie is also discussed.

Push-out test of headed stud connectors subjected to freeze-thaw cycles and artificial corrosion

To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel–concrete composite structures under the influence of freeze–thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.

Fatigue behavior of unidirectional fiber‐reinforced pultruded composites with high volume fiber fraction

AbstractPultrusion is a high‐volume manufacturing process for fiber‐reinforced polymer (FRP) composites ensuring high strength and quality products. However, research studies are very limited on the fatigue behavior of these products, especially with unidirectional fiber alignment. This study investigates the fatigue behavior of the unidirectional pultruded glass FRP (GFRP) composites with high fiber volume fraction ( ). Tension–tension fatigue loading was applied with different levels of applied stress, frequency, and gripping condition until failure. Results showed that the high composites have significantly low fatigue life cycle. Moreover, increasing the frequency showed better fatigue resistance, while the tabs geometry has insignificant effect on the fatigue behavior of the dog‐bone shaped specimens. Comparison with available literature showed that GFRP composites with high have lower fatigue performance than those with low . A fatigue capacity reduction factor is also proposed for unidirectional GFRP composites as a function of the .

Structural reliability and partial safety factor assessment of unreinforced masonry in vertical bending

ABSTRACT This paper focuses on a structural reliability-based assessment of clay brick unreinforced masonry (URM) walls subjected to uniformly distributed out-of-plane loads in one-way vertical bending. Stochastic models combining finite element analysis (FEA) and Monte Carlo simulations (MCS) are used to account for spatial variability of the flexural tensile bond strength when estimating the wall failure loads. The strength of URM walls is known to be influenced by the flexural tensile bond strength, which is subject to high spatial variability as batching, workmanship, and environmental exposure alter the strength of this bond. For this assessment, single skin walls have been considered with bond strength statistics seen in typical construction. The model error statistics available for similar walls are combined with the results of the spatial stochastic FEA and probabilistic load models to determine the reliability index corresponding to the Australian Standard for Masonry Structures AS 3700 design of members in vertical bending. It was found that existing levels of reliability exceed target reliabilities, and the capacity reduction factor can be increased from 0.60 to 0.65 for URM walls in one-way vertical bending while still providing an acceptable level of reliability. A sensitivity analysis showed this finding to be robust.

Seismic Capacity Estimation for Composite Multi-storeyed RC buildings

Seismic hazard happens to be one of the most devastative natural hazards to be faced by mankind. In view of urbanization and knowledge gained from past natural hazards, several urban cities have seen a transformation in building their habitats. These range from regular, irregular multistoried Reinforced Concrete (RC) buildings to several composite multi storeyed RC buildings due to certain inherent functional benefits (viz., ventilation, parking space, ease of construction etc.,). The existing seismic code regulations provided by BIS (Bureau of Indian Standards) do not specify any approach to arrive at appropriate design seismic forces and capacity for composite multi storeyed buildings. Therefore, it is imminent to assess the structural behaviour of these multistoried composite RC buildings under earthquake forces at the site location to provide a safe and functional configuration. Hence an attempt has been made in this study to analytically compare regular and composite RC building models having similar Plan and Height. The multistoried RC building configurations considered in this study comprises of regular RC building as well as RC building frame coupled with steel joists at certain locations to represent a composite structural system. These models are further analyzed to arrive at inherent nonlinear seismic capacity, ductility and design seismic forces necessary to be considered during design of RC building structure. Hence, a typical hypothetical G+5 regular and composite multistoried buildings were modelled and analysed using the nonlinear static (pushover analysis) approach. The outcomes of these analyses clearly portrays the variation in dynamic characteristics of the building frames represented in terms of its time period, inelastic capacity and response reduction factor (R). Moreover, the present study emphasizes to analytically evaluate the design seismic forces necessary for earthquake resistant design of composite buildings in any urban environment albeit the changes in structural configurations.

Climatic influence on productivity of walking excavators and bulldozers in stripping in gold placer mining

The state and mineability of placer gold reserves and resources in the Russian Federation is reviewed. Judging from wide application of dragline excavators in peat cutting, it can be effective to use draglines in placer mining at depths up to 50 m due to the much lower cost of stripping compared to the other methods. In this case, it is possible to apply various schemes of direct dumping and wider employment of draglines in actual mining. It is noted that one of the highest influences on productivity of draglines and bulldozers during stripping is the presence of seasonal and perennial frost. Two groups of factors to decrease productivity of walking excavators and bulldozers at negative air temperatures are proposed. The conclusions are made about the difficulty of determining frozen ground cuttability due to the peculiarities of overburden sediment formation and because of deficient detailed studies into the properties of rocks, which govern their strength characteristics during freezing. The less labor-intensive method of calculating productivity reduction of walking excavators and bulldozers during stripping is proposed as the determination of hourly productivity reduction patterns by mathematical methods describing the random nature of phenomena, in particular, by the correlation method. The equations of the hourly productivity reduction of draglines and bulldozers depending on average monthly negative air temperature and the hourly capacity reduction factor as function of seasonal permafrost thickness and perennial permafrost cross-sections in overburden face are derived. It is noted that seasonal freezing governs reduction in productivity of excavators and bulldozers at the beginning of the warm period of the year until the permafrost is completely thawed. Stefan’s formula is suggested, according to which it is possible to calculate the depths of seasonal freezing of peat depending on the average monthly air temperature quite reliably.

Design of thin steel battens subject to pull-through failures

Localized pull-through failures of cold-formed steel roof battens have often been observed at the roof batten to purlin/rafter/truss screw connections during storms and cyclones. Recent research studies have therefore proposed improved design capacity equations by undertaking both experimental studies and finite element analyses. However, they have not investigated the effects of very thin steel roof and ceiling battens (<0.50 mm), safety lip features and purlin flexibility on the localized pull-through failures. Hence this study was aimed at investigating the effects of all such practical design issues and to assess the suitability of current design equations. For this purpose, a series of static and fatigue pull-through failure tests of roof and ceiling battens was undertaken under simulated static and cyclic wind uplift loads. This paper presents the details and results obtained from this study including suitable design recommendations. It has shown that the recently developed pull-through capacity equations can be used for very thin steel battens. Higher capacity reduction factors are recommended for use with these design equations for battens made of Australian cold-formed steels used in this study. The use of safety lip features did not affect the static pull-through capacities, but it improved the fatigue performance of roof battens. Finally, the suitability of using low strength steel battens instead of high strength steel battens was evaluated.

Reliability updating of partial factors for empirical codes: Application to Super-T PSC girders designs at the ultimate limit state in bending

Reliability design code calibrations typically involve the comparison of calculated levels of safety (β) of designs to a range of prospective partial safety factors with the minimum acceptable level of safety (βT). When updating the calibration and the original βT is unknown or undocumented, design-specific probability models and the code-implied level of safety are necessary. This study presents a methodology for updating capacity reduction factors ϕ for a suite of PSC bridge girder section designs for ultimate strength in bending for a design code for which βT is unknown. In the methodology, the code-implied safety as inferred from the notional traffic design load, and the designed girder safety under actual traffic loading are computed. The method is applied to the suite of prestressed concrete Super-T girders designed to the Australian bridge standards AS5100, in which the implicit βT is not known. The results find both code-implied safety and designed girder safety far surpasses the usual recommendations for βT for all designs and regardless of ϕ. As such, only through the relative comparison of code-implied safety and designed girder safety can recommendations be made on increasing ϕ in AS 5100 for Super-T girder ultimate strength in bending. Moreover, the comparison with code-implied safety is taken to indicate the desired degree of reserve capacity available for future traffic growth. The results inform on possible improvements for the next version of AS5100. More significantly, the work illustrates a way to reliability-update partial factors of design codes when βT is not known, and future-proofing structures is seen as necessary.

Model error and reliability of reinforced concrete beams in shear designed according to the Modified Compression Field Theory

AbstractModel error (or model uncertainty) were probabilistically characterized for modified compression field theory (MCFT) Simplified and General Method approaches using experimental databases that contained reinforced concrete (RC) beams having shear failures with and without stirrups (168 and 368 specimens, respectively). It was found that when compared to the design shear model currently used in ACI‐318, the General Method produced low model error variability indicating better consistency for the determination of shear strength. Structural reliabilities were then calculated for RC beams in shear designed to MCFT General Method (AASHTO LRFD, CSA A23.3‐14, AS3600‐2018) for a live‐to‐dead load ratio between 0 and 5, and for capacity reduction factor ϕ = 0.70, 0.75, and 0.80. It was concluded that the ϕ‐factor for shear failure for Australian standards can be increased from 0.70 to 0.75 for RC beams with stirrups, providing a 7.1% increase in the design shear capacity and contributing to sustainable design and reduction in greenhouse gas emissions due to more efficient usage of materials.

Experiments of cast-in anchors under simulated seismic loads

This paper presents a series of tests of cast-in anchors subjected to simulated seismic loads, including 19 shear tests and 17 tension tests. The specimens were subjected to both monotonic and displacement-controlled quasi-static cyclic loading. The anchors under cyclic loading showed strength degradation, especially towards the later stages of loading with relatively large displacement levels. Anchors controlled by steel fracture in shear had significant strength reduction, which was attributed to bending in anchor shafts caused by progressive concrete damage. The cyclic tests were added to a database of 114 tests (11 from this study) in shear and 22 tests (8 from this study) in tension. These available tests of cast-in anchors indicated that the existing seismic reduction factor of 0.75 in ACI 318 failure is conservative for concrete breakout failure mode. Meanwhile, a capacity reduction factor for anchors with steel failure in shear seems necessary, and a reduction factor of 0.75 is suggested though further study is needed to better understand the related behavior.

POST-EARTHQUAKE CAPACITY EVALUATION OF RC FRAME STRUCTURES WITH MULTI-STORY FLEXURAL WALLS

After an earthquake, it is important to evaluate the residual seismic capacity of damaged buildings in order to determine the necessity of repair and retrofit and to make an efficient recovery plan. In this regard, a Japanese guideline developed by the Japan Building Disaster Prevention Association (JBPDA) “Standard for Post-earthquake Damage Level Classification of Buildings 1) ” is currently in use in Japan to estimate the residual seismic capacity of structures based on an index named R. The R-index represents the ratio of seismic capacity before and after the earthquake. The R-index calculation is intended to be a simple seismic evaluation method that does not require complicated analysis. However, this simplified method is based on the assumption that the ultimate deformation capacity of all members is the same; thus, it is not practical for assessing dual systems, such as reinforced concrete (RC) buildings containing both moment resisting frames and walls. The main objective of this study is to propose a new evaluation method to determine the R-index for buildings of mixed structure types. The proposed method uses two factors: (i) explicit consideration of different deformation capacities of structural members, θu, and (ii) a seismic capacity reduction factor, ηW 7) which considers the hysteretic energy absorption reduction of each structural member based on the observed level of damage. The available JBDPA method and the proposed method are assessed using results obtained from a shake-table test of an RC building.

Shear strength reduction of aluminium lipped channel beams due to web openings

Aluminium members are recently being used as main structural elements in residential, commercial and industrial buildings. Aluminium Lipped Channel Beam (LCB) is one of the popular thin-walled sections used in different applications in construction. Web openings are incorporated in these sections to accommodate building services when they are used as beams. Even though the bending, shear and web crippling behaviours of these sections were investigated in the past, their structural behaviour with web openings have not been investigated. Hence, experimental and numerical studies were conducted in this research to investigate the shear behaviour of these aluminium LCBs with web openings. An aspect ratio of one was considered in this study. A total of 17 tests were conducted first to investigate the shear behaviour of aluminium LCBs with circular web openings using three-point loading arrangement. Finite element models were developed with appropriate loading and boundary conditions and validated using the experimental results. A detailed parametric study was then undertaken using the currently available roll-formed aluminium LCBs with different thicknesses, grades and web opening sizes. The ultimate shear capacities and the shear capacity reduction factors obtained from the tests and finite element analyses were compared with the currently available design rules. This paper presents the details and results of the experimental and numerical studies on the shear behaviour of aluminium LCBs with circular web openings and the comparison with current and recently proposed design rules.