Mahmud Ashraf - Academia.edu (original) (raw)
Papers by Mahmud Ashraf
Applied Mechanics and Materials, 2016
ABSTRACT Fire following earthquake (FFE) is a serious threat to structures that are partially dam... more ABSTRACT Fire following earthquake (FFE) is a serious threat to structures that are partially damaged in a prior earthquake potentially leading to a quick collapse of the structure. The majority of standards and codes for the design of structures against earthquake, however, ignore the possibility of FFE and thus buildings designed with those codes fail swiftly when exposed to fire after earthquake. A sequential structural analysis based on FEMA 356 is performed here on the Immediate Occupancy (IO) and the Life Safety (LS) performance levels of two reinforced concrete frames. The frames are first subjected to an earthquake load with a Peak Ground Acceleration (PGA) of .30g. This is followed by a fire analysis, using ISO 834 and natural fire curves. The time taken for the structures weakened by the earthquake to collapse under these fires is then found through a robust numerical analysis. As a benchmark, fire-only analyses are also performed for undamaged structures. The results show that earthquake-weakened structures are more vulnerable to fire than undamaged structures, to the extent that the fire resistance of the damaged structures can decline to about a third of the original undamaged structures. The results also show that the fire resistance of the frame exposed to the natural fire differs from that of the frame exposed to the ISO 834 fire. This is due to the inclusion of parameters such as dimensions of the compartment as well as thermal properties of the combustible materials and the size and position of opening in the natural fire model, which does not exist in the ISO 834. Whilst the investigation is conducted for a certain class of structures (regular buildings, reinforced concrete frames, 3 stories), the results confirm the need for the incorporation of FFE into the process of analysis and design, and provides some quantitative measures on the level of associated effects.
The Structural Engineer, Jun 28, 2005
Thin Walled Structures, Oct 1, 2006
Stainless steel&a... more Stainless steel's characteristic nonlinear, rounded stress–strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more pronounced than that of ordinary carbon steel and hence appropriate modelling of the cold-worked corner regions is very important. Despite the importance of geometrical imperfections, their measurement is not a very common practice and assumed models are generally adopted in
ABSTRACT Stainless steel structural sections possess several features that result in a significan... more ABSTRACT Stainless steel structural sections possess several features that result in a significantly different response to that of equivalent carbon steel sections. To date these features have not been fully recognized in design codes, which have largely adapted rules devised for carbon steel in a rather simplistic fashion. Recently, a new approach for dealing with local buckling and the associated loss of effectiveness that does not utilize the concepts of either cross-sectional classification or effective cross-sectional properties has been developed for stainless steel and has also been applied to other nonlinear metallic materials. The method is based directly on the deformation capacities of cross sections and covers the behavior of stainless steel members subjected to flexural buckling and combined axial load plus bending. The proposed method has been verified using test results and its performance has been compared against the existing ASCE and Eurocode design guidance for structural stainless steel. Significantly improved and more consistent predictions have been obtained using the proposed method without any extra calculation effort.
Thin-Walled Structures, 2016
ABSTRACT Stainless steel exhibits nonlinear material behaviour which requires somewhat different ... more ABSTRACT Stainless steel exhibits nonlinear material behaviour which requires somewhat different treatment from the elastic, perfectly-plastic model often used for carbon steel. Moreover, its response to cold-working is far more pronounced when compared to that of carbon steel. Stainless steel columns should therefore be designed using an appropriate material model to include proper allowance for coldworking. The performance of existing design codes – Eurocode 3 Part 1.4 and ASCE 8-02 - has been investigated by comparison against all available test results on stainless steel columns. The observed conservatism and scatter in predictions have led to the formulation of a new set of column curves which are based on a more precise material definition. The basic description by a Perry-Robertson format was retained but modified to include the effects of strain hardening. Predictions from this new approach have been found to be both more accurate and more consistent than the existing codes.
The Continuous Strength Method (CSM) is a recently developed strain based design method, which in... more The Continuous Strength Method (CSM) is a recently developed strain based design method, which incorporates material nonlinearity as well as exploits pronounced strain hardening observed in stainless steel. CSM is shown to perform well at the cross-section level for relatively stocky sections. The current study primarily aims to extend the scope of CSM to include slender sections as typically available stainless steel products fall into this category. A numerical investigation is carried out for stainless steel slender sections subjected to combined loading i.e. compression plus bending. Nonlinear FE models were developed and validated using available experimental results and were consequently used to generate additional results for a wider range of cross-section slenderness. Keeping the basic design philosophy in line with the current CSM design technique, a number of modifications are proposed herein for accurate prediction of the beam-column interaction observed in slender stainl...
Structural stainless steel requires appropriate recognition of its characteristic material proper... more Structural stainless steel requires appropriate recognition of its characteristic material properties when used in construction. A new design method called the Continuous Strength Method (CSM) exploits the beneficial properties through a strain based approach, which is primarily aimed for stocky cross-sections. It is, however, worth noting that typically available stainless steel cross-sections are quite slender, and hence proposals are made herein to extend the scope of CSM for slender cross-sections. The current paper numerically investigates the flexural buckling behaviour of stainless steel members, and proposes an approach that combines the CSM concept for predicting cross-sectional resistances with Perry type formulations adopted in Eurocode for flexural buckling. Nonlinear FE models were developed and were subsequently used to generate additional results for welded I sections subjected to buckling about major and minor axes. Finally, column curves are proposed following Perry...
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
Fourth International Conference on Advances in Steel Structures, 2005
ABSTRACT Geometric imperfections are an inevitable and a potentially significant parameter requir... more ABSTRACT Geometric imperfections are an inevitable and a potentially significant parameter required when modelling the behaviour of structural members. Despite their importance, measurement of imperfections is not a very common practice. In previous numerical modelling studies a number of assumed models have been adopted – often without proper verification. This paper evaluates previous research in this field, examines the applicability of existing models using numerical techniques and identifies the most suitable ones. After careful investigation specific proposals are made for both the distribution and the magnitude of local geometric imperfections in stainless steel cross-sections. These proposals have been verified by comparing the numerically obtained load-deformation behaviour to that obtained experimentally.
Tubular Structures XIV, 2012
Research and Applications in Structural Engineering, Mechanics and Computation, 2013
Stainless steel&a... more Stainless steel's characteristic nonlinear, rounded stress–strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more pronounced than that of ordinary carbon steel and hence appropriate modelling of the cold-worked corner regions is very important. Despite the importance of geometrical imperfections, their measurement is not a very common practice and assumed models are generally adopted in
Journal of Scientific Research, 2012
Engineering Structures, 2014
ABSTRACT Stainless steel is gaining widespread use in construction due to its obvious special cha... more ABSTRACT Stainless steel is gaining widespread use in construction due to its obvious special characteristics – attractive appearance, corrosion resistance and ease of maintenance, whilst beneficial mechanical properties such as high ductility, better fire resistance than carbon steel and high strength demonstrated by the duplex grades add value to its aesthetics. Reliable experimental investigation is a prerequisite to explore the full potential of stainless steel members and to evaluate the performance of the existing design rules. The current study describes a test program on cold-formed stainless steel square hollow section (SHS) members subjected to eccentric compression to examine the beam–column interaction, which is one of the least explored fields in structural stainless steel. Cross-sections are produced from duplex stainless steel grade with the measured yield stress up to 700 MPa, for which material properties were obtained by tensile coupons cut from within the cross-sections. A total of 20 specimens are tested with initial geometric imperfection being measured at mid-height of each beam–column specimen. The specimens were placed between knife-edge supports to simulate an ideal pin-ended boundary condition at both ends. The column lengths were 550 and 1100 mm, and each specimen was subjected to compression loading with eccentricity varying from 0 to 60 mm. The test results were compared with those predicted using the American and the Australian/New Zealand design specifications for cold-formed stainless steel structures. It is observed that the code predictions are mostly conservative for stainless steel beam–columns with rooms for improvement in the current design guidance.
Proceedings of the 10th International Conference on Advances in Steel Concrete Composite and Hybrid Structures, 2012
Sustainable infrastructure development is an inseparable part for a sustainable urban transformat... more Sustainable infrastructure development is an inseparable part for a sustainable urban transformation. An appropriate assessment tool along with a suitable interpretation framework is necessary to achieve the sustainability goals of social, environmental and economic criteria. Available commercial sustainability rating systems are mostly focused on building systems such as LEED rating system, green star rating system etc. Current research explores the opportunity to introduce a sustainability phase model based infrastructure ...
Applied Mechanics and Materials, 2016
ABSTRACT Fire following earthquake (FFE) is a serious threat to structures that are partially dam... more ABSTRACT Fire following earthquake (FFE) is a serious threat to structures that are partially damaged in a prior earthquake potentially leading to a quick collapse of the structure. The majority of standards and codes for the design of structures against earthquake, however, ignore the possibility of FFE and thus buildings designed with those codes fail swiftly when exposed to fire after earthquake. A sequential structural analysis based on FEMA 356 is performed here on the Immediate Occupancy (IO) and the Life Safety (LS) performance levels of two reinforced concrete frames. The frames are first subjected to an earthquake load with a Peak Ground Acceleration (PGA) of .30g. This is followed by a fire analysis, using ISO 834 and natural fire curves. The time taken for the structures weakened by the earthquake to collapse under these fires is then found through a robust numerical analysis. As a benchmark, fire-only analyses are also performed for undamaged structures. The results show that earthquake-weakened structures are more vulnerable to fire than undamaged structures, to the extent that the fire resistance of the damaged structures can decline to about a third of the original undamaged structures. The results also show that the fire resistance of the frame exposed to the natural fire differs from that of the frame exposed to the ISO 834 fire. This is due to the inclusion of parameters such as dimensions of the compartment as well as thermal properties of the combustible materials and the size and position of opening in the natural fire model, which does not exist in the ISO 834. Whilst the investigation is conducted for a certain class of structures (regular buildings, reinforced concrete frames, 3 stories), the results confirm the need for the incorporation of FFE into the process of analysis and design, and provides some quantitative measures on the level of associated effects.
The Structural Engineer, Jun 28, 2005
Thin Walled Structures, Oct 1, 2006
Stainless steel&a... more Stainless steel's characteristic nonlinear, rounded stress–strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more pronounced than that of ordinary carbon steel and hence appropriate modelling of the cold-worked corner regions is very important. Despite the importance of geometrical imperfections, their measurement is not a very common practice and assumed models are generally adopted in
ABSTRACT Stainless steel structural sections possess several features that result in a significan... more ABSTRACT Stainless steel structural sections possess several features that result in a significantly different response to that of equivalent carbon steel sections. To date these features have not been fully recognized in design codes, which have largely adapted rules devised for carbon steel in a rather simplistic fashion. Recently, a new approach for dealing with local buckling and the associated loss of effectiveness that does not utilize the concepts of either cross-sectional classification or effective cross-sectional properties has been developed for stainless steel and has also been applied to other nonlinear metallic materials. The method is based directly on the deformation capacities of cross sections and covers the behavior of stainless steel members subjected to flexural buckling and combined axial load plus bending. The proposed method has been verified using test results and its performance has been compared against the existing ASCE and Eurocode design guidance for structural stainless steel. Significantly improved and more consistent predictions have been obtained using the proposed method without any extra calculation effort.
Thin-Walled Structures, 2016
ABSTRACT Stainless steel exhibits nonlinear material behaviour which requires somewhat different ... more ABSTRACT Stainless steel exhibits nonlinear material behaviour which requires somewhat different treatment from the elastic, perfectly-plastic model often used for carbon steel. Moreover, its response to cold-working is far more pronounced when compared to that of carbon steel. Stainless steel columns should therefore be designed using an appropriate material model to include proper allowance for coldworking. The performance of existing design codes – Eurocode 3 Part 1.4 and ASCE 8-02 - has been investigated by comparison against all available test results on stainless steel columns. The observed conservatism and scatter in predictions have led to the formulation of a new set of column curves which are based on a more precise material definition. The basic description by a Perry-Robertson format was retained but modified to include the effects of strain hardening. Predictions from this new approach have been found to be both more accurate and more consistent than the existing codes.
The Continuous Strength Method (CSM) is a recently developed strain based design method, which in... more The Continuous Strength Method (CSM) is a recently developed strain based design method, which incorporates material nonlinearity as well as exploits pronounced strain hardening observed in stainless steel. CSM is shown to perform well at the cross-section level for relatively stocky sections. The current study primarily aims to extend the scope of CSM to include slender sections as typically available stainless steel products fall into this category. A numerical investigation is carried out for stainless steel slender sections subjected to combined loading i.e. compression plus bending. Nonlinear FE models were developed and validated using available experimental results and were consequently used to generate additional results for a wider range of cross-section slenderness. Keeping the basic design philosophy in line with the current CSM design technique, a number of modifications are proposed herein for accurate prediction of the beam-column interaction observed in slender stainl...
Structural stainless steel requires appropriate recognition of its characteristic material proper... more Structural stainless steel requires appropriate recognition of its characteristic material properties when used in construction. A new design method called the Continuous Strength Method (CSM) exploits the beneficial properties through a strain based approach, which is primarily aimed for stocky cross-sections. It is, however, worth noting that typically available stainless steel cross-sections are quite slender, and hence proposals are made herein to extend the scope of CSM for slender cross-sections. The current paper numerically investigates the flexural buckling behaviour of stainless steel members, and proposes an approach that combines the CSM concept for predicting cross-sectional resistances with Perry type formulations adopted in Eurocode for flexural buckling. Nonlinear FE models were developed and were subsequently used to generate additional results for welded I sections subjected to buckling about major and minor axes. Finally, column curves are proposed following Perry...
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
Fourth International Conference on Advances in Steel Structures, 2005
ABSTRACT Geometric imperfections are an inevitable and a potentially significant parameter requir... more ABSTRACT Geometric imperfections are an inevitable and a potentially significant parameter required when modelling the behaviour of structural members. Despite their importance, measurement of imperfections is not a very common practice. In previous numerical modelling studies a number of assumed models have been adopted – often without proper verification. This paper evaluates previous research in this field, examines the applicability of existing models using numerical techniques and identifies the most suitable ones. After careful investigation specific proposals are made for both the distribution and the magnitude of local geometric imperfections in stainless steel cross-sections. These proposals have been verified by comparing the numerically obtained load-deformation behaviour to that obtained experimentally.
Tubular Structures XIV, 2012
Research and Applications in Structural Engineering, Mechanics and Computation, 2013
Stainless steel&a... more Stainless steel's characteristic nonlinear, rounded stress–strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more pronounced than that of ordinary carbon steel and hence appropriate modelling of the cold-worked corner regions is very important. Despite the importance of geometrical imperfections, their measurement is not a very common practice and assumed models are generally adopted in
Journal of Scientific Research, 2012
Engineering Structures, 2014
ABSTRACT Stainless steel is gaining widespread use in construction due to its obvious special cha... more ABSTRACT Stainless steel is gaining widespread use in construction due to its obvious special characteristics – attractive appearance, corrosion resistance and ease of maintenance, whilst beneficial mechanical properties such as high ductility, better fire resistance than carbon steel and high strength demonstrated by the duplex grades add value to its aesthetics. Reliable experimental investigation is a prerequisite to explore the full potential of stainless steel members and to evaluate the performance of the existing design rules. The current study describes a test program on cold-formed stainless steel square hollow section (SHS) members subjected to eccentric compression to examine the beam–column interaction, which is one of the least explored fields in structural stainless steel. Cross-sections are produced from duplex stainless steel grade with the measured yield stress up to 700 MPa, for which material properties were obtained by tensile coupons cut from within the cross-sections. A total of 20 specimens are tested with initial geometric imperfection being measured at mid-height of each beam–column specimen. The specimens were placed between knife-edge supports to simulate an ideal pin-ended boundary condition at both ends. The column lengths were 550 and 1100 mm, and each specimen was subjected to compression loading with eccentricity varying from 0 to 60 mm. The test results were compared with those predicted using the American and the Australian/New Zealand design specifications for cold-formed stainless steel structures. It is observed that the code predictions are mostly conservative for stainless steel beam–columns with rooms for improvement in the current design guidance.
Proceedings of the 10th International Conference on Advances in Steel Concrete Composite and Hybrid Structures, 2012
Sustainable infrastructure development is an inseparable part for a sustainable urban transformat... more Sustainable infrastructure development is an inseparable part for a sustainable urban transformation. An appropriate assessment tool along with a suitable interpretation framework is necessary to achieve the sustainability goals of social, environmental and economic criteria. Available commercial sustainability rating systems are mostly focused on building systems such as LEED rating system, green star rating system etc. Current research explores the opportunity to introduce a sustainability phase model based infrastructure ...