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F. Wald

Czech Technical University in Prague, Department of Steel and Timber Structures, Faculty Member

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Works at Czech Technical University in Prague as Professor and Head of the Department steel and timber structures. In his professional life he concentrates to the connection and fire design of steel structures. After Sept 11 studied experimentally the robustness of multi-storey building in Cardington on the experimental seven-storey building. Served as Chairman of the EU COST TU action Integrated fire engineering and response (IFER) which focussed to cooperation between the research community and fire brigades. In structural steel connection design prepared the component model for column bases and the component based finite element model of joints. Works in ECCS TC 10 Structural joints and in Project team for preparation of EN1993-1-8:2020.

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Papers by F. Wald

Connections of Trapezoidal Sheets under Fire

Acta Polytechnica, 2009

This paper describes two different experiments on connections of trapezoidal sheets under elevate... more This paper describes two different experiments on connections of trapezoidal sheets under elevated temperatures. The first experiments were tensile tests carried out on four sets of tests with screwed connections under ambient and elevated temperatures. One diameter of self-drilling screws and three different thicknesses of trapezoidal sheets were used. The applied screws were without washers, or with sealed or steel washers. The second experiment was performed in a laboratory furnace to check the catenary action of a thin-walled trapezoidal sheet. The basic theory tested in this experiment was that in the first phase of the fire the sheet behaves as a simply supported beam, while in the second phase the load bearing is transferred by a tension membrane. These experiments will be used to develop a design model of connections at high temperatures. High fire resistance of the trapezoidal sheet, dependent on suitable design of the screwed connection to the bearing structure, was confir...

Temperature of Steel Columns under Natural Fire

Acta Polytechnica, 2004

Current fire design models for time-temperature development within structural elements as well as... more Current fire design models for time-temperature development within structural elements as well as for structural behaviour are based on isolated member tests subjected to standard fire regimes, which serve as a reference heating, but do not model natural fire. Only tests on a real structure under a natural fire can evaluate future models of the temperature developments in a fire compartment, of the transfer of heat into the structure and of the overall structural behaviour under fire.To study overall structural behaviour, a research project was conducted on an eight storey steel frame building at the Cardington Building Research Establishment laboratory on January 16, 2003. A fire compartment 11×7 m was prepared on the fourth floor. A fire load of 40 kg/m2 was applied with 100 % permanent mechanical load and 65 % of imposed load. The paper summarises the experimental programme and shows the temperature development of the gas in the fire compartment and of the fire protected columns...

Modelling of Joints of Sandwiches Panels

The lightweight sandwiches panels are produced by a modern and environmental controlled technolog... more The lightweight sandwiches panels are produced by a modern and environmental controlled technology. A typical sandwich panel consist of two covering steel sheets, generally made of the trapezoidal or light profiled steel sheets, and of a weak lightweight core. The increasing use of lightweight sandwiches panels in industrial and civil buildings requires the development of suitable methods for analysis. The response of single panel as well as behaviour of whole structure is influenced by joints between sandwiches panels and framework. The stiffening effect of the cladding panels on the structural behaviour of the structure, the stress skin procedure, with the respect to the connections was evaluated in [3] to observe the behaviour under the seismic loading. The published analysis [1] neglects stress distribution between the both metal faces. Only inner sheet is assumed to carry the applied loads and the bearing capacity of the connection, see [2].

Advanced analysis of members with gusset plate joints

Modern Trends in Research on Steel, Aluminium and Composite Structures, 2021

Concrete in compression and base plate in bending

In this paper, the concrete underneath the base plate together with the base plate is referred to... more In this paper, the concrete underneath the base plate together with the base plate is referred to as "component concrete in compression and base plate in bending" or in short "concrete in compression". Models are presented for the determination of the resistance and stiffness of this component. The models have been validated with tests. The paper also presents finite element calculations that provide additional validation. The predicted resistances according to ENV 1993-1-1 are conservative with a margin of 1.4 to 2.5 to the test results. The stiffness of the concrete in compression depends on the quality of the execution. In case of good workmanship, there is reasonable agreement between the measured and the predicted stiffness.

Component method for steel column bases

Heron

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Horizontal forces in steel structures tested in fire

Journal of Constructional Steel Research, 2009

Fire tests carried out on the eight-storey steel framed building at the Building Research Establi... more Fire tests carried out on the eight-storey steel framed building at the Building Research Establishment's Cardington laboratory have shown that the connections are subject to large axial force. These forces are the result of thermal movements of the structure during heating and cooling and in some cases can result in failure of the structure. This paper describes a fire test carried out on the steel frame at Cardington on 16th January 2003 and a fire test carried out on a structure in Ostrava on 16th June 2006. In both cases the tests were designed to measure the forces generated in the connections.

Stresses in steel columns under natural fire

... The beam to beam connections were created by fin plates, steel S275. ... Multi-linear isotrop... more

Fire damaged structures

This chapter is concerned with technical aspects of appraisal of fire damaged steel, concrete and... more This chapter is concerned with technical aspects of appraisal of fire damaged steel, concrete and stone structures. The assessment of fire damages to structures follows a similar general process as appraisal of existing structures. It is possible to restore a fire damaged structure to its original load carrying capacity. In making a decision about repairing a fire damaged building, considerations should be given to aesthetic appearance, the reliability of repairs, the views of insurance company and the client, in addition to technical feasibility. For member states of the European Union, safety requirements in case of fire are based on the Construction Products Directive (Council Directive 89/106/EEC: 21.12.1988). The Directive is applied to construction products as the essential requirement in respect of construction works. In Annex I of the Directive, the essential requirements for mechanical resistance and stability, and for fire safety, are summarised. The construction works must be designed and built in such a way that, in the event of an outbreak of fire: x The load-bearing capacity of the construction can be assumed for a specific period of time; x The generation and spread of fire and smoke within the works are limited; x The spread of the fire to neighbouring construction works is limited; x Occupants can leave the works or be rescued by other means; x The safety of rescue teams is taken into consideration. The load-bearing capacity of the construction may be modelled on the principles summarised in the parts of the structural Eurocodes which deal with fire. Fire resistance is commonly used to characterize the performance of elements of structure in fire. It may be defined as the time for which elements of a structure satisfactorily perform their required functions under specified fire conditions. These functions may include the ability to avoid collapse, to limit the spread of fire and to support other elements. All construction materials progressively lose their ability to support a load when they are heated. If components of any structure are heated sufficiently they may collapse. The consequences of such a collapse vary, depending on how critical the component is in controlling the overall behaviour of the structure. In order to limit the threat posed by fire to people in a building, and to reduce the damage that a fire may inflict, large buildings may be divided into smaller fire compartments using fire-resisting walls and floors. Parts of a fire compartment may be further divided to protect the building from particular hazards within them. The performance of fire separating elements may rely on the ability of their supporting structure to continue to provide support under fire conditions. The criticality of an element is the degree to which its collapse would affect the performance of the structure as a whole. All of the main components of a structure are generally expected to exhibit fire resistance proportionate to the nature of the perceived risk. The nature of the risk is usually assessed on the basis of the size and proposed use of the building of which the structural element is a part; this is an important part of a fire safety risk analysis.

Experimental investigation of panel zone in steel beam-to-column joint at elevated temperature

Structures & Architecture

Connection Temperatures during the Mokrsko Fire Test

The Mokrsko fire test focused on the overall behaviour of the structure, which cannot be observed... more The Mokrsko fire test focused on the overall behaviour of the structure, which cannot be observed on the separate elements, and also on the temperature of connections with improved fire resistance. During the test, measurements were made of the temperature of the gas and of the elements, the overall and relative deformations, gas pressure, humidity, the radiation of the compartment to structural element and the external steel column, transport of the moisture through the walls, and also the climatic conditions. The results of the test show the differences between the behaviour of the element and the behaviour of the structure exposed to high temperatures during a fire. The collapse of the composite slab was reached. The results of the numerical simulations using the SAFIR program compared well with the measured temperature values in the structure and also in the connections.

Steel column base classification

The influence of the rotational characteristics of the column bases on the structural frame respo... more

Steel and composite joints

Component method for steel column base plates

Temperature of External Column During Fire Test

Component based Finite Element Design of Seismically Qualified Joints

Journal of Physics: Conference Series

This paper describes the principles of Component Based Finite Element Modelling (CBFEM) and the s... more This paper describes the principles of Component Based Finite Element Modelling (CBFEM) and the system response quantity and application features for design of prequalified joints for seismic applications. The elements are analysed by geometrically and materially non-linear analysis with imperfections (GMNIA). The proper behaviour of components, e.g. of bolts, anchor bolts, welds etc., is treated by introducing components representing its behaviour in term of initial stiffness, ultimate resistance and deformation capacity. To show this process a contribution is prepared, which summarises the history of achievements of FEA application in structural connections. Contribution shows the currents trends in advanced modelling of connection components and differences of the research oriented and design-oriented models. Both have their roles in advanced analyses.

Column bases in shear and normal force

Connections of steel columns to concrete foundations may be loaded by combinations of normal forc... more Connections of steel columns to concrete foundations may be loaded by combinations of normal force, bending moment and shear force. Shear force will primarily be transmitted by friction between the base plate and the grout layer to the concrete foundation. If the compression force is small, or if tension force is present, as may occur in slender high rise structures like towers and masts, the friction will be small or absent. Then, the anchor bolts will be loaded by shear force and bending moment.

Numerical study of travelling fire in full-scale experimental building

Research and Applications in Structural Engineering, Mechanics and Computation, 2013

Embedded steel column bases

Journal of Constructional Steel Research, 2000

Testing and numerical modelling of embedded steel column bases are discussed in this paper. The b... more Testing and numerical modelling of embedded steel column bases are discussed in this paper. The behaviour of two different types of experimental specimen has been analysed. The specimens were specifically designed so that the bond and punching resistances of the steel column bases could be quantified. Numerical modelling by the finite element method (FEM) has been conducted to investigate the stress distributions in column bases. The numerical results have been calibrated against the test results. The testing and numerical modelling described provide a basis for establishing a design model that will be introduced in Part II of this paper.

Stiffness of cover plate connections with slotted holes

Journal of Constructional Steel Research, 2004

This paper describes the prediction of stiffness of bolted cover plate connections with slots per... more

Connections of Trapezoidal Sheets under Fire

Acta Polytechnica, 2009

This paper describes two different experiments on connections of trapezoidal sheets under elevate... more This paper describes two different experiments on connections of trapezoidal sheets under elevated temperatures. The first experiments were tensile tests carried out on four sets of tests with screwed connections under ambient and elevated temperatures. One diameter of self-drilling screws and three different thicknesses of trapezoidal sheets were used. The applied screws were without washers, or with sealed or steel washers. The second experiment was performed in a laboratory furnace to check the catenary action of a thin-walled trapezoidal sheet. The basic theory tested in this experiment was that in the first phase of the fire the sheet behaves as a simply supported beam, while in the second phase the load bearing is transferred by a tension membrane. These experiments will be used to develop a design model of connections at high temperatures. High fire resistance of the trapezoidal sheet, dependent on suitable design of the screwed connection to the bearing structure, was confir...

Temperature of Steel Columns under Natural Fire

Acta Polytechnica, 2004

Current fire design models for time-temperature development within structural elements as well as... more Current fire design models for time-temperature development within structural elements as well as for structural behaviour are based on isolated member tests subjected to standard fire regimes, which serve as a reference heating, but do not model natural fire. Only tests on a real structure under a natural fire can evaluate future models of the temperature developments in a fire compartment, of the transfer of heat into the structure and of the overall structural behaviour under fire.To study overall structural behaviour, a research project was conducted on an eight storey steel frame building at the Cardington Building Research Establishment laboratory on January 16, 2003. A fire compartment 11×7 m was prepared on the fourth floor. A fire load of 40 kg/m2 was applied with 100 % permanent mechanical load and 65 % of imposed load. The paper summarises the experimental programme and shows the temperature development of the gas in the fire compartment and of the fire protected columns...

Modelling of Joints of Sandwiches Panels

The lightweight sandwiches panels are produced by a modern and environmental controlled technolog... more The lightweight sandwiches panels are produced by a modern and environmental controlled technology. A typical sandwich panel consist of two covering steel sheets, generally made of the trapezoidal or light profiled steel sheets, and of a weak lightweight core. The increasing use of lightweight sandwiches panels in industrial and civil buildings requires the development of suitable methods for analysis. The response of single panel as well as behaviour of whole structure is influenced by joints between sandwiches panels and framework. The stiffening effect of the cladding panels on the structural behaviour of the structure, the stress skin procedure, with the respect to the connections was evaluated in [3] to observe the behaviour under the seismic loading. The published analysis [1] neglects stress distribution between the both metal faces. Only inner sheet is assumed to carry the applied loads and the bearing capacity of the connection, see [2].

Advanced analysis of members with gusset plate joints

Modern Trends in Research on Steel, Aluminium and Composite Structures, 2021

Concrete in compression and base plate in bending

In this paper, the concrete underneath the base plate together with the base plate is referred to... more In this paper, the concrete underneath the base plate together with the base plate is referred to as "component concrete in compression and base plate in bending" or in short "concrete in compression". Models are presented for the determination of the resistance and stiffness of this component. The models have been validated with tests. The paper also presents finite element calculations that provide additional validation. The predicted resistances according to ENV 1993-1-1 are conservative with a margin of 1.4 to 2.5 to the test results. The stiffness of the concrete in compression depends on the quality of the execution. In case of good workmanship, there is reasonable agreement between the measured and the predicted stiffness.

Component method for steel column bases

Heron

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Horizontal forces in steel structures tested in fire

Journal of Constructional Steel Research, 2009

Fire tests carried out on the eight-storey steel framed building at the Building Research Establi... more Fire tests carried out on the eight-storey steel framed building at the Building Research Establishment's Cardington laboratory have shown that the connections are subject to large axial force. These forces are the result of thermal movements of the structure during heating and cooling and in some cases can result in failure of the structure. This paper describes a fire test carried out on the steel frame at Cardington on 16th January 2003 and a fire test carried out on a structure in Ostrava on 16th June 2006. In both cases the tests were designed to measure the forces generated in the connections.

Stresses in steel columns under natural fire

... The beam to beam connections were created by fin plates, steel S275. ... Multi-linear isotrop... more

Fire damaged structures

This chapter is concerned with technical aspects of appraisal of fire damaged steel, concrete and... more This chapter is concerned with technical aspects of appraisal of fire damaged steel, concrete and stone structures. The assessment of fire damages to structures follows a similar general process as appraisal of existing structures. It is possible to restore a fire damaged structure to its original load carrying capacity. In making a decision about repairing a fire damaged building, considerations should be given to aesthetic appearance, the reliability of repairs, the views of insurance company and the client, in addition to technical feasibility. For member states of the European Union, safety requirements in case of fire are based on the Construction Products Directive (Council Directive 89/106/EEC: 21.12.1988). The Directive is applied to construction products as the essential requirement in respect of construction works. In Annex I of the Directive, the essential requirements for mechanical resistance and stability, and for fire safety, are summarised. The construction works must be designed and built in such a way that, in the event of an outbreak of fire: x The load-bearing capacity of the construction can be assumed for a specific period of time; x The generation and spread of fire and smoke within the works are limited; x The spread of the fire to neighbouring construction works is limited; x Occupants can leave the works or be rescued by other means; x The safety of rescue teams is taken into consideration. The load-bearing capacity of the construction may be modelled on the principles summarised in the parts of the structural Eurocodes which deal with fire. Fire resistance is commonly used to characterize the performance of elements of structure in fire. It may be defined as the time for which elements of a structure satisfactorily perform their required functions under specified fire conditions. These functions may include the ability to avoid collapse, to limit the spread of fire and to support other elements. All construction materials progressively lose their ability to support a load when they are heated. If components of any structure are heated sufficiently they may collapse. The consequences of such a collapse vary, depending on how critical the component is in controlling the overall behaviour of the structure. In order to limit the threat posed by fire to people in a building, and to reduce the damage that a fire may inflict, large buildings may be divided into smaller fire compartments using fire-resisting walls and floors. Parts of a fire compartment may be further divided to protect the building from particular hazards within them. The performance of fire separating elements may rely on the ability of their supporting structure to continue to provide support under fire conditions. The criticality of an element is the degree to which its collapse would affect the performance of the structure as a whole. All of the main components of a structure are generally expected to exhibit fire resistance proportionate to the nature of the perceived risk. The nature of the risk is usually assessed on the basis of the size and proposed use of the building of which the structural element is a part; this is an important part of a fire safety risk analysis.

Experimental investigation of panel zone in steel beam-to-column joint at elevated temperature

Structures & Architecture

Connection Temperatures during the Mokrsko Fire Test

The Mokrsko fire test focused on the overall behaviour of the structure, which cannot be observed... more The Mokrsko fire test focused on the overall behaviour of the structure, which cannot be observed on the separate elements, and also on the temperature of connections with improved fire resistance. During the test, measurements were made of the temperature of the gas and of the elements, the overall and relative deformations, gas pressure, humidity, the radiation of the compartment to structural element and the external steel column, transport of the moisture through the walls, and also the climatic conditions. The results of the test show the differences between the behaviour of the element and the behaviour of the structure exposed to high temperatures during a fire. The collapse of the composite slab was reached. The results of the numerical simulations using the SAFIR program compared well with the measured temperature values in the structure and also in the connections.

Steel column base classification

The influence of the rotational characteristics of the column bases on the structural frame respo... more

Steel and composite joints

Component method for steel column base plates

Temperature of External Column During Fire Test

Component based Finite Element Design of Seismically Qualified Joints

Journal of Physics: Conference Series

This paper describes the principles of Component Based Finite Element Modelling (CBFEM) and the s... more This paper describes the principles of Component Based Finite Element Modelling (CBFEM) and the system response quantity and application features for design of prequalified joints for seismic applications. The elements are analysed by geometrically and materially non-linear analysis with imperfections (GMNIA). The proper behaviour of components, e.g. of bolts, anchor bolts, welds etc., is treated by introducing components representing its behaviour in term of initial stiffness, ultimate resistance and deformation capacity. To show this process a contribution is prepared, which summarises the history of achievements of FEA application in structural connections. Contribution shows the currents trends in advanced modelling of connection components and differences of the research oriented and design-oriented models. Both have their roles in advanced analyses.

Column bases in shear and normal force

Connections of steel columns to concrete foundations may be loaded by combinations of normal forc... more Connections of steel columns to concrete foundations may be loaded by combinations of normal force, bending moment and shear force. Shear force will primarily be transmitted by friction between the base plate and the grout layer to the concrete foundation. If the compression force is small, or if tension force is present, as may occur in slender high rise structures like towers and masts, the friction will be small or absent. Then, the anchor bolts will be loaded by shear force and bending moment.

Numerical study of travelling fire in full-scale experimental building

Research and Applications in Structural Engineering, Mechanics and Computation, 2013

Embedded steel column bases

Journal of Constructional Steel Research, 2000

Testing and numerical modelling of embedded steel column bases are discussed in this paper. The b... more Testing and numerical modelling of embedded steel column bases are discussed in this paper. The behaviour of two different types of experimental specimen has been analysed. The specimens were specifically designed so that the bond and punching resistances of the steel column bases could be quantified. Numerical modelling by the finite element method (FEM) has been conducted to investigate the stress distributions in column bases. The numerical results have been calibrated against the test results. The testing and numerical modelling described provide a basis for establishing a design model that will be introduced in Part II of this paper.

Stiffness of cover plate connections with slotted holes

Journal of Constructional Steel Research, 2004

This paper describes the prediction of stiffness of bolted cover plate connections with slots per... more