The knowledge of earthquake load in the last 50 years has been changing according to the results ... more The knowledge of earthquake load in the last 50 years has been changing according to the results of the research. In national codes and provisions of European Union, Japan, U.S., duration of most bridges is supposed to be 50 years. Thus, bridges built 30 or more years ago are designed to load that is different from today's knowledge of earthquake load. Many bridges which were built before 1970s which are still in use in either Europe or Japan or the U.S. have been designed with little or with no any consideration for seismic demand. Majority of these bridges lack the ductility and strength to resist earthquakes. Meanwhile strong earthquakes have revealed all vulnerable places and wrong detailing on almost all bridges built in seismic regions more than fifty years ago. After the 1971 San Fernando earthquake the U.S. for the first time in the world started seismic retrofit programs for bridges. Japan also started similar programs, especially after the 1995 Kobe earthquake. European Union may not be out of this global problem and must have own retrofit programs for bridges. Thousands of existing bridges all over the word built more than fifty years ago in earthquake zones are still in operation waiting to be retrofitted in order to withstand earthquake loading defined as a result of up to data of research. In this sense in this paper some solutions, recommendations and comments for retrofitting and rapid recovery of bridges after earthquake using the latest concepts for structural upgrading is presented as the main goal to contribute to the knowledge for an earthquake resilient society.
Emergency functionality and rapid recovery of road networks after a strong intensity earthquake t... more Emergency functionality and rapid recovery of road networks after a strong intensity earthquake that has triggered additional hazards such as post-earthquake fires, landslides, tsunamis, bridge collapses and a series of large aftershocks is a vital requirement for the sustainability of any modern society, which, in the light of recent earthquake events, has not yet been properly addressed. In most national codes and provisions duration of bridges is supposed to be at least 50 years. Design codes must be based on functionality criteria rather than safety. Some bridges which were built before 1970s which are still in use in either Europe or Japan or the U.S. have been designed with little or with no any consideration for seismic demand. Majority of these bridges lack the ductility and strength to resist earthquakes. Meanwhile strong motion earthquakes have revealed all vulnerable places and wrong detailing on almost all bridges built in seismically active regions more than fifty years...
U radu je prikazana analiza djelovanja seizmickih sila na okvirnu celicnu konstrukciju koja je iz... more U radu je prikazana analiza djelovanja seizmickih sila na okvirnu celicnu konstrukciju koja je izvedena i patentirana u Svedskoj. Konstruktivni sustav za kojeg je provedena analiza prvotno je bio sacinjen od okvirne celicne konstrukcije sa armiranobetonskom jezgrom. Kako bi se ostvarilo trosenje seizmicke energije nelinearnim ponasanjem, konstrukcija je „omeksana“ zamjenom armiranobetonske jezgre celicnom jezgrom. Prikljucci su modelirani kao nepopustljivi (rigid), kako bi se sprijecile rotacije između konstruktivnih elemenata, te su primijenjeni kriteriji „zgrade posmika“. Konstrukcija je analizirana primjenom dviju linearnih metoda: ekvivalentnog statickog djelovanja i modalnom analizom, te primjenom dviju nelinearnih metoda: nelinearnom statickom metodom (N2) i nelinearnom dinamickom metodom u vremenu (time history). Na kraju je napravljena usporedba rezultata dobivenih ovim metodama te je analiziran utjecaj nelinearnosti na horizontalne apsolutne i relativne pomake katova konstr...
Shortly after the opening of Dubrovnik (Croatia) cable-stayed bridge in 2002 the violent vibratio... more Shortly after the opening of Dubrovnik (Croatia) cable-stayed bridge in 2002 the violent vibrations of the bridge deck, pylon and cables in a strong wind "Bora" combined with light rain were observed about twelve times a year. This paper analyses effect of violent vibrations of cables and their influence on the overall dynamic behaviour of cable-stayed bridge. Firstly, the vibration of a massive cable which is connected to a vibrating cable-stayed bridge deck and pylon is presented analytically. Equations describing a change of the cable's force and its eigenvalues due to the cable’s undamped and damped vibrations are also derived. Mathematical lamped models substituting the behaviour of a massive bridge cable and its effect on the dynamic properties of the overall cable-stayed bridge is presented. Finally, the measures for Dubrovnik bridge rehabilitation are presented in a way of suppressing cables vibrations by devices. After installing the Maurer Adaptive Cable Damp...
U knjizi su prezentirani samo neki najvažniji dijelovi iz obimne raspoložive literature publicira... more U knjizi su prezentirani samo neki najvažniji dijelovi iz obimne raspoložive literature publicirane u svijetu koja obrađuje probleme stabilnosti građevinskih konstrukcija. Sadržaj knjige podijeljen je u tri dijela. U I. dijelu izvedene su jednadžbe statike konstrukcija prema teoriji 2. reda. Pritom su rijeseni slucajevi kako pojedinacnih stapova konstantnog i promjenljivog poprecnog presjeka, tako i sustava pravih stapova konstantnog poprecnog presjeka. Statika konstrukcija po teoriji 2. reda je nelinearna, a prezentirana je prema metodi deformacija, koja je kao pojam korisniku knjige poznata vec od ranije kada su u kolegiju Građevna statika rađeni izracuni po linearnim teorijama. U rjesenju statike konstrukcija po teoriji 2. reda uvedena je geometrijska nelinearnost. Gradivo izloženo u I. dijelu knjige bilo je podlogom da se u II. dijelu knjige problem stabilnosti konstrukcija tretira kao homogeni problem statike konstrukcija po teoriji 2. reda, sto znaci da se u objasnjenju nacina...
U radu je provedena analiza ponašanja tankostjenog hrpta neukrućene zavarene grede na utjecaj jed... more U radu je provedena analiza ponašanja tankostjenog hrpta neukrućene zavarene grede na utjecaj jednoliko raspodijeljenog vertikalnog opterećenja. Izrađen je numerički model grede u programskom paketu ABAQUS. Cilj ovog rada je dobiti vjernu numeričku simulaciju ponašanja grede u usporedbi s laboratorijski ispitanom gredom čiji su rezultati ispitivanja preuzeti iz literature te analizirati pojavu izbočivanja u zoni panela hrpta. Provedena je linearna analiza kojom su određeni vlastiti oblici izbočivanja grede te nelinearna analiza kojom su određene vrijednosti deformiranja grede. Na kraju je dana usporedba rezultata dobivenih numeričkim simulacijama s rezultatima laboratorijskog ispitivanja.
ABSTRACTIt is well known that seismic links are usually designed to remain in elastic region duri... more ABSTRACTIt is well known that seismic links are usually designed to remain in elastic region during ordinary loading but withstand nonlinear deformation during seismic event having capability to dissipate seismic energy. The use of short seismic links is recommended because they are capable of dissipating seismic energy in larger quantity by shear, while the webs in these links are expected to yield in shear during large seismic events, i.e. dissipation of seismic energy by bending in links is negligible. Shear deformations are basically plane deformations of the cross section web of the link, without any significant tendency towards lateral torsional buckling. To achieve the required plastic rotation, local instabilities such as flange or web buckling should be delayed. The flange local buckling is delayed by specifying width to thickness ratio, while the web local buckling will be prevented by adding number of transverse stiffeners along the web of the link. The main purpose of th...
The aim of this paper is the development of the two different numerical techniques for the preloa... more The aim of this paper is the development of the two different numerical techniques for the preloading of bolts by the finite element method using the software Abaqus Standard. Furthermore, this paper gave detailed guidelines for modelling contact, method for solving the numerical error problems such as numerical singularity error and negative eigenvalues due to rigid body motion or the problem of the extensive elongation of bolts after pretension which is occurring during the analysis. The behaviour of bolted joints depending on the two different approaches of pretension was shown on the example of an extended end-plate bolted beam-to-column connection under the monotonic loading. The behaviour of beam-to-column connection was shown in the form and moment-rotation (M-ϕ) curves and validated by experimental test. Advantages and disadvantages of pretension techniques, as well as the speed of numerical models, were also presented in this paper.
In this paper the nonlinear static seismic analysis of typical steel framed structure including t... more In this paper the nonlinear static seismic analysis of typical steel framed structure including the real joint stiffness (instead of traditionally design with pinned or rigid joints) is presented. In order to take into account the real joint behaviour in seismic analysis nonlinear analysis using the finite element method of welded beam-to-column joint was carried out firstly. The beam-to-column joints of analysed structure was chosen according to experimental tests. The results of finite element analysis obtained in program Abaqus 6.12 are shown in the form of the moment-rotation curve. Nonlinear moment-rotation curve will be idealized by tree-linear curve for the purpose of seismic analysis. The idea of this research is to show the influence of semi-rigid joints on the seismic effects for moment resisting frames. The storey drifts and displacements obtained from seismic analysis for steel frame including semi-rigid joints will be compared with results for steel frame with tradition...
Beam-to-column joints of steel frames traditionally have been modelled either as ideally pinned o... more Beam-to-column joints of steel frames traditionally have been modelled either as ideally pinned or ideally perfectly rigid. This paper presents the seismic analysis of typical steel framed structure including the influence of real joint stiffness. In the first part of analysis the real rigid joints have been introduced, but in the second part the analysis of frames with semi-rigid joints will be presented. The aim of this paper is to show the difference between results obtained from analysis according to Eurocode 8-1 (nonlinear static N2 method) including the previously mentioned joint stiffness (rigid and semi- rigid) for absolute and relative displacements of stores
This paper presents the results of research in reliability of short seismic links in shear based ... more This paper presents the results of research in reliability of short seismic links in shear based on tests. Four types of short links were analysed, each having the same cross section and the same length, but with different number of web stiffeners. The main purpose of the stiffeners is to preserve buckling of the seismic link web, i.e. to achieve plastification of the cross section by shear. The design model of shear resistance according to Eurocode 8 is applicable only to short links without web stiffeners. By adding the web stiffeners nonlinear inelastic behaviour of short seismic links differs depending on the number of stiffeners, so that the calculation model of shear resistance according to Eurocode 8 for short seismic link with stiffeners should be improved. This fact is considered by introducing the improve factors that were determined from the laboratory tests conducted on 16 specimens. On the base of tests in the second part of this paper the reliability of short seismic link is performed by forming limit state equations. These equations are formed by using the stochastic model, i.e. by describing the statistical nature of basic variables calculating the reliability index as an operational value of failure probability. The reliability level was determined by using the probabilistic analysis based on the first order reliability method (FORM) which resulted with the conclusion that the short seismic links with two and three couples of web stiffeners designed according to requirements of Eurocode 8 have enough reliability for the reliability class RC2 and the mean recurrence interval (MRI) of 50 years.
Predstavljena je nova konstruktivna tipologija hibridnog okvira s ekscentricnim dijagonalama za p... more Predstavljena je nova konstruktivna tipologija hibridnog okvira s ekscentricnim dijagonalama za primjenu u seizmickim podrucjima, koja se temelji na ukrucivanju okvira bez dijagonala s ekscentricno prikljucenim dijagonalama. Opisano je ponasanje najvažnijeg segmenta grede okvira nazvanog "seizmicka spona", preko koje se gubi seizmicka energija. Prikazani su rezultati eksperimentalnih ispitivanja na okvirima u cjelini, te na seizmickim sponama kao izdvojenim dijelovima konstrukcije. Na kraju je dan prijedlog za dopunom europske norme Eurokod 8-1.
In most national codes and provisions duration of bridges is at least 50 years. Some bridges whic... more In most national codes and provisions duration of bridges is at least 50 years. Some bridges which were built before 1970s either in Europe or Japan or the US have been designed with little or with no any consideration for seismic demand. Majority of these bridges were supported by reinforced concrete bents and pier walls that lack the ductility and strength to resist earthquakes. Meanwhile strong motion earthquakes have revealed all vulnerable places on each of those bridges if built in seismically active regions. After the 1971 San Fernando earthquake the US started several seismic retrofit programs. Retrofit programs in the 1980s included the first use of isolators on bridges and a program to retrofit single-column bents. These programs were greatly accelerated after the 1989 Santa Cruz (Loma Prieta) and 1994 Northridge earthquakes. After the 1994 Northridge earthquake it was observed that no serious damage would have occurred if the previous retrofit program had already been imp...
The knowledge of earthquake load in the last 50 years has been changing according to the results ... more The knowledge of earthquake load in the last 50 years has been changing according to the results of the research. In national codes and provisions of European Union, Japan, U.S., duration of most bridges is supposed to be 50 years. Thus, bridges built 30 or more years ago are designed to load that is different from today's knowledge of earthquake load. Many bridges which were built before 1970s which are still in use in either Europe or Japan or the U.S. have been designed with little or with no any consideration for seismic demand. Majority of these bridges lack the ductility and strength to resist earthquakes. Meanwhile strong earthquakes have revealed all vulnerable places and wrong detailing on almost all bridges built in seismic regions more than fifty years ago. After the 1971 San Fernando earthquake the U.S. for the first time in the world started seismic retrofit programs for bridges. Japan also started similar programs, especially after the 1995 Kobe earthquake. European Union may not be out of this global problem and must have own retrofit programs for bridges. Thousands of existing bridges all over the word built more than fifty years ago in earthquake zones are still in operation waiting to be retrofitted in order to withstand earthquake loading defined as a result of up to data of research. In this sense in this paper some solutions, recommendations and comments for retrofitting and rapid recovery of bridges after earthquake using the latest concepts for structural upgrading is presented as the main goal to contribute to the knowledge for an earthquake resilient society.
Emergency functionality and rapid recovery of road networks after a strong intensity earthquake t... more Emergency functionality and rapid recovery of road networks after a strong intensity earthquake that has triggered additional hazards such as post-earthquake fires, landslides, tsunamis, bridge collapses and a series of large aftershocks is a vital requirement for the sustainability of any modern society, which, in the light of recent earthquake events, has not yet been properly addressed. In most national codes and provisions duration of bridges is supposed to be at least 50 years. Design codes must be based on functionality criteria rather than safety. Some bridges which were built before 1970s which are still in use in either Europe or Japan or the U.S. have been designed with little or with no any consideration for seismic demand. Majority of these bridges lack the ductility and strength to resist earthquakes. Meanwhile strong motion earthquakes have revealed all vulnerable places and wrong detailing on almost all bridges built in seismically active regions more than fifty years...
U radu je prikazana analiza djelovanja seizmickih sila na okvirnu celicnu konstrukciju koja je iz... more U radu je prikazana analiza djelovanja seizmickih sila na okvirnu celicnu konstrukciju koja je izvedena i patentirana u Svedskoj. Konstruktivni sustav za kojeg je provedena analiza prvotno je bio sacinjen od okvirne celicne konstrukcije sa armiranobetonskom jezgrom. Kako bi se ostvarilo trosenje seizmicke energije nelinearnim ponasanjem, konstrukcija je „omeksana“ zamjenom armiranobetonske jezgre celicnom jezgrom. Prikljucci su modelirani kao nepopustljivi (rigid), kako bi se sprijecile rotacije između konstruktivnih elemenata, te su primijenjeni kriteriji „zgrade posmika“. Konstrukcija je analizirana primjenom dviju linearnih metoda: ekvivalentnog statickog djelovanja i modalnom analizom, te primjenom dviju nelinearnih metoda: nelinearnom statickom metodom (N2) i nelinearnom dinamickom metodom u vremenu (time history). Na kraju je napravljena usporedba rezultata dobivenih ovim metodama te je analiziran utjecaj nelinearnosti na horizontalne apsolutne i relativne pomake katova konstr...
Shortly after the opening of Dubrovnik (Croatia) cable-stayed bridge in 2002 the violent vibratio... more Shortly after the opening of Dubrovnik (Croatia) cable-stayed bridge in 2002 the violent vibrations of the bridge deck, pylon and cables in a strong wind "Bora" combined with light rain were observed about twelve times a year. This paper analyses effect of violent vibrations of cables and their influence on the overall dynamic behaviour of cable-stayed bridge. Firstly, the vibration of a massive cable which is connected to a vibrating cable-stayed bridge deck and pylon is presented analytically. Equations describing a change of the cable's force and its eigenvalues due to the cable’s undamped and damped vibrations are also derived. Mathematical lamped models substituting the behaviour of a massive bridge cable and its effect on the dynamic properties of the overall cable-stayed bridge is presented. Finally, the measures for Dubrovnik bridge rehabilitation are presented in a way of suppressing cables vibrations by devices. After installing the Maurer Adaptive Cable Damp...
U knjizi su prezentirani samo neki najvažniji dijelovi iz obimne raspoložive literature publicira... more U knjizi su prezentirani samo neki najvažniji dijelovi iz obimne raspoložive literature publicirane u svijetu koja obrađuje probleme stabilnosti građevinskih konstrukcija. Sadržaj knjige podijeljen je u tri dijela. U I. dijelu izvedene su jednadžbe statike konstrukcija prema teoriji 2. reda. Pritom su rijeseni slucajevi kako pojedinacnih stapova konstantnog i promjenljivog poprecnog presjeka, tako i sustava pravih stapova konstantnog poprecnog presjeka. Statika konstrukcija po teoriji 2. reda je nelinearna, a prezentirana je prema metodi deformacija, koja je kao pojam korisniku knjige poznata vec od ranije kada su u kolegiju Građevna statika rađeni izracuni po linearnim teorijama. U rjesenju statike konstrukcija po teoriji 2. reda uvedena je geometrijska nelinearnost. Gradivo izloženo u I. dijelu knjige bilo je podlogom da se u II. dijelu knjige problem stabilnosti konstrukcija tretira kao homogeni problem statike konstrukcija po teoriji 2. reda, sto znaci da se u objasnjenju nacina...
U radu je provedena analiza ponašanja tankostjenog hrpta neukrućene zavarene grede na utjecaj jed... more U radu je provedena analiza ponašanja tankostjenog hrpta neukrućene zavarene grede na utjecaj jednoliko raspodijeljenog vertikalnog opterećenja. Izrađen je numerički model grede u programskom paketu ABAQUS. Cilj ovog rada je dobiti vjernu numeričku simulaciju ponašanja grede u usporedbi s laboratorijski ispitanom gredom čiji su rezultati ispitivanja preuzeti iz literature te analizirati pojavu izbočivanja u zoni panela hrpta. Provedena je linearna analiza kojom su određeni vlastiti oblici izbočivanja grede te nelinearna analiza kojom su određene vrijednosti deformiranja grede. Na kraju je dana usporedba rezultata dobivenih numeričkim simulacijama s rezultatima laboratorijskog ispitivanja.
ABSTRACTIt is well known that seismic links are usually designed to remain in elastic region duri... more ABSTRACTIt is well known that seismic links are usually designed to remain in elastic region during ordinary loading but withstand nonlinear deformation during seismic event having capability to dissipate seismic energy. The use of short seismic links is recommended because they are capable of dissipating seismic energy in larger quantity by shear, while the webs in these links are expected to yield in shear during large seismic events, i.e. dissipation of seismic energy by bending in links is negligible. Shear deformations are basically plane deformations of the cross section web of the link, without any significant tendency towards lateral torsional buckling. To achieve the required plastic rotation, local instabilities such as flange or web buckling should be delayed. The flange local buckling is delayed by specifying width to thickness ratio, while the web local buckling will be prevented by adding number of transverse stiffeners along the web of the link. The main purpose of th...
The aim of this paper is the development of the two different numerical techniques for the preloa... more The aim of this paper is the development of the two different numerical techniques for the preloading of bolts by the finite element method using the software Abaqus Standard. Furthermore, this paper gave detailed guidelines for modelling contact, method for solving the numerical error problems such as numerical singularity error and negative eigenvalues due to rigid body motion or the problem of the extensive elongation of bolts after pretension which is occurring during the analysis. The behaviour of bolted joints depending on the two different approaches of pretension was shown on the example of an extended end-plate bolted beam-to-column connection under the monotonic loading. The behaviour of beam-to-column connection was shown in the form and moment-rotation (M-ϕ) curves and validated by experimental test. Advantages and disadvantages of pretension techniques, as well as the speed of numerical models, were also presented in this paper.
In this paper the nonlinear static seismic analysis of typical steel framed structure including t... more In this paper the nonlinear static seismic analysis of typical steel framed structure including the real joint stiffness (instead of traditionally design with pinned or rigid joints) is presented. In order to take into account the real joint behaviour in seismic analysis nonlinear analysis using the finite element method of welded beam-to-column joint was carried out firstly. The beam-to-column joints of analysed structure was chosen according to experimental tests. The results of finite element analysis obtained in program Abaqus 6.12 are shown in the form of the moment-rotation curve. Nonlinear moment-rotation curve will be idealized by tree-linear curve for the purpose of seismic analysis. The idea of this research is to show the influence of semi-rigid joints on the seismic effects for moment resisting frames. The storey drifts and displacements obtained from seismic analysis for steel frame including semi-rigid joints will be compared with results for steel frame with tradition...
Beam-to-column joints of steel frames traditionally have been modelled either as ideally pinned o... more Beam-to-column joints of steel frames traditionally have been modelled either as ideally pinned or ideally perfectly rigid. This paper presents the seismic analysis of typical steel framed structure including the influence of real joint stiffness. In the first part of analysis the real rigid joints have been introduced, but in the second part the analysis of frames with semi-rigid joints will be presented. The aim of this paper is to show the difference between results obtained from analysis according to Eurocode 8-1 (nonlinear static N2 method) including the previously mentioned joint stiffness (rigid and semi- rigid) for absolute and relative displacements of stores
This paper presents the results of research in reliability of short seismic links in shear based ... more This paper presents the results of research in reliability of short seismic links in shear based on tests. Four types of short links were analysed, each having the same cross section and the same length, but with different number of web stiffeners. The main purpose of the stiffeners is to preserve buckling of the seismic link web, i.e. to achieve plastification of the cross section by shear. The design model of shear resistance according to Eurocode 8 is applicable only to short links without web stiffeners. By adding the web stiffeners nonlinear inelastic behaviour of short seismic links differs depending on the number of stiffeners, so that the calculation model of shear resistance according to Eurocode 8 for short seismic link with stiffeners should be improved. This fact is considered by introducing the improve factors that were determined from the laboratory tests conducted on 16 specimens. On the base of tests in the second part of this paper the reliability of short seismic link is performed by forming limit state equations. These equations are formed by using the stochastic model, i.e. by describing the statistical nature of basic variables calculating the reliability index as an operational value of failure probability. The reliability level was determined by using the probabilistic analysis based on the first order reliability method (FORM) which resulted with the conclusion that the short seismic links with two and three couples of web stiffeners designed according to requirements of Eurocode 8 have enough reliability for the reliability class RC2 and the mean recurrence interval (MRI) of 50 years.
Predstavljena je nova konstruktivna tipologija hibridnog okvira s ekscentricnim dijagonalama za p... more Predstavljena je nova konstruktivna tipologija hibridnog okvira s ekscentricnim dijagonalama za primjenu u seizmickim podrucjima, koja se temelji na ukrucivanju okvira bez dijagonala s ekscentricno prikljucenim dijagonalama. Opisano je ponasanje najvažnijeg segmenta grede okvira nazvanog "seizmicka spona", preko koje se gubi seizmicka energija. Prikazani su rezultati eksperimentalnih ispitivanja na okvirima u cjelini, te na seizmickim sponama kao izdvojenim dijelovima konstrukcije. Na kraju je dan prijedlog za dopunom europske norme Eurokod 8-1.
In most national codes and provisions duration of bridges is at least 50 years. Some bridges whic... more In most national codes and provisions duration of bridges is at least 50 years. Some bridges which were built before 1970s either in Europe or Japan or the US have been designed with little or with no any consideration for seismic demand. Majority of these bridges were supported by reinforced concrete bents and pier walls that lack the ductility and strength to resist earthquakes. Meanwhile strong motion earthquakes have revealed all vulnerable places on each of those bridges if built in seismically active regions. After the 1971 San Fernando earthquake the US started several seismic retrofit programs. Retrofit programs in the 1980s included the first use of isolators on bridges and a program to retrofit single-column bents. These programs were greatly accelerated after the 1989 Santa Cruz (Loma Prieta) and 1994 Northridge earthquakes. After the 1994 Northridge earthquake it was observed that no serious damage would have occurred if the previous retrofit program had already been imp...
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Papers by Mladen Bulić