Simplified FEM modelling for the collapse assessment of a masonry vault

 

Simplified FEM modelling for the collapse assessment
of a masonry vault

Pierluigi Olmati
Sapienza University of Rome, Italy (now at TAISEI Corp., Tokyo, Japan)
pierluigi.olmati@gmail.com

Konstantinos Gkoumas
Sapienza University of Rome, Italy (now at European Commission, Joint Research Centre)
konstantinos.gkoumas@uniroma1.it, https://orcid.org/0000-0003-3833-6223

Franco Bontempi
Sapienza University of Rome, Italy
franco.bontempi@uniroma1.it, https://orcid.org/0000-0001-6377-7501

ABSTRACT. This study is motivated from the collapse of an old masonry building in the Southern Italy. FEM analyses are carried out focusing on the influence of the contrasting wall on the stability of the vault. In the analyses, the structure is subjected to a damage scenario on the contrasting wall due to a demolition project, and the consequence of the damage is evaluated using the explicit dynamic simulation made by Ls-Dyna®. A micro modelling technique (discrete FEM model) is adopted to model the masonry: the mortar is modelled by contact surfaces between the masonry units, which are explicitly modelled by blocks of meshes. This modelling technique is proven to be effective to predict the collapse behavior of the structure.

KEYWORDS. FEM; Masonry structures; Forensic investigations; Vault structures.

Coupling effects between wind and train transit induced fatigue damage in suspension bridges

Coupling effects between wind and train transit induced fatigue damage in suspension bridges

Petrini F 1), Olmati P 2), Bontempi F 1)

1) Department of Structural and Geotechnical Engineering, Sapienza University of Rome, Via Eudossiana 18, Rome, Italy

2) Taisei Corporation, Shinjuku Center Building, Nishi Shinjuku 1-25-1, Tokyo, Japan

Abstract 

Long-span steel suspension bridges develop significant vibrations under the effect of external time-variable loadings because their slenderness. This causes significant stresses variations that could induce fatigue problems in critical components of the bridge. The research outcome presented in this paper includes a fatigue analysis of a long suspension bridge with 3300 meters central suspended span under wind action and train transit. Special focus is made on the counterintuitive interaction effects between train and wind loads in terms of fatigue damage accumulation in the hanger ropes. In fact the coupling of the two actions is shown to have positive effects for some hangers in terms of damage accumulation. Fatigue damage is evaluated using a linear accumulation model (Palmgren-Miner rule), analyses are carried out in time domain by a three-dimensional non-linear finite element model of the bridge. Rational explanation regarding the above-mentioned counterintuitive behavior is given on the basis of the stress time histories obtained for pertinent hangers under the effects of wind and train as acting separately or simultaneously. The interaction between wind and train traffic loads can be critical for some hanger ropes therefore interaction phenomena within loads should be considered in the design.

Keywords: suspension bridges; fatigue analysis; wind-train interaction; damage accumulation; non-linearity

Safety factor for structural elements subjected to impulsive blast loads

Safety factor forstructural elements subjected to impulsive blast loads

Pierluigi Olmati^1a*, Dimitrios Vamvatsikos^2b, Mark G. Stewart^3c

¹ Department of Architecture and Wind Engineering, Tokyo Polytechnic University, Japan.

² School of Civil Engineering, National Technical University of Athens, Greece.

³ Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia.

^a Researcher, fellow of the Japanese Society for the Promotion of Science JSPS.

^b Assistant Professor.

^c Professor and Director.

^* Corresponding author; e-mail: pierluigi.olmati@gmail.com  

Abstract

Design of blast loaded structures is usually carried out following a deterministic rather than a probabilistic approach. The design load scenario would cover the plausible load conditions (typically some conservative estimate) that a structure would experience if an explosion occurs but the probability that the structure will satisfy the design performances for the considered scenario remains unknown. Applying a performance-based design framework typically requires arduous Monte Carlo simulations, but a probabilistic design could also be achieved by a single structural analysis when consistent safety factors are applied to the load and the structural resistance. Such a factor is proposed herein for the case of components subjected to impulsive blast loads. The dependence of the safety factor on the amount of explosive, stand-off distance and their variability is estimated numerically and provided by means of regression formulas. A design example using the proposed safety factor is carried out and Monte Carlo simulation is used for verification. The results confirm the validity of the proposed safety factor approach and its applicability for the performance-based design of blast loaded structures using the current design practice methods.

Keywords: performance-based design; probabilistic analysis; safety factor; blast design; terroristic explosions; blast load; vehicle borne improvised explosive devices.

Figure 16: Probability of exceeding the limit state P(ϴ>θ) calculated using a Monte Carlo simulation compared with the APE used in the design carried out with the proposed safety factor λ. The structural uncertainties have been considered as well for comparison purpose.  Furthermore the reinforcement percentage is plotted too as design output for the RC panel. The proposed approach is accurate enough for APEs<15% while for higher APEs (not suitable for design purposes) it gives a conservative design.

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Fragility analysis for ballistic design

Fragility analysis for ballistic design

Patrick Trasborg, Clay Naito, Paolo Bocchini & Pierluigi Olmati

Patrick Trasborg, Clay Naito, Paolo Bocchini & Pierluigi Olmati (2016):
Fragility analysis for ballistic design, Structure and Infrastructure Engineering, DOI:
10.1080/15732479.2016.1244209

To link to this article: http://dx.doi.org/10.1080/15732479.2016.1244209

ABSTRACT

Effective structural design to resist ballistic effects such as small arms or fragmenting weapons has been a goal since weapons were developed. Approaches currently in use for ballistic design are predominantly deterministic and allow designers to decide what wall thickness should be used to stop a prescribed projectile impacting at a predefined velocity. The research presented in this paper provides a framework for conducting reliability analysis of structures subjected to bullet and fragment demands. Thus, pseudofragility curves are developed for the limit states related to spall and perforation of wall panels, residual velocities of bullets and fragments, and injury to personnel. The pseudo-fragility analysis provides engineers and owners with a tool to quickly assess the reliability of a wall system subjected to high velocity, low mass projectiles. In particular, the proposed analysis method allows designers and owners to determine the probability of spall and perforation, residual velocity, and injury as a function of wall thickness or threat standoff distance.

Simplified reliability analysis of punching in reinforced concrete flat slab buildings under accidental actions

Simplified reliability analysis of punching in reinforced concrete flat slab buildings under accidental actions

P. Olmati (a), J. Sagaseta (b), D. Cormie (c), A.E.K. Jones (c)
a University of Surrey, UK2 - Currently at Tokyo Polytechnic University (JSPS fellow)
b Department of Civil and Environmental Engineering, University of Surrey, Guildford, UK
c Arup, London, UK

Olmati P, Sagaseta J, Cormie D, Jones AEK, Simplified reliability analysis of punching in reinforced concrete flat slab buildings under accidental actions, Engineering Structures, Vol. 130, pp. 83-98, 2017.

Abstract

Flat slab concrete buildings are widely found in infrastructure such as office and residential buildings or industrial facilities. The susceptibility of progressive collapse of such structures due to accidental loads is highly dependent on the structural performance of the slab-column connections. This paper presents a framework for a simplified reliability analysis and derivation of safety factors for computing the probability of punching of flat slab concrete buildings subjected to accidental loads such as column removal, slab falling from above or blast load. The main advantage of the proposed approach is that it considers in a simple manner, the uncertainty in the gravity load applied in the slab before the accidental event, which affects the inertial effects and demand/capacity ratio in the slab-column connections. Eurocode 2 and the Critical Shear Crack Theory for punching are used and extended to dynamic cases for the assessment of the demand/capacity ratio using computer-based time history finite element simulations. The proposed reliability method is applied to a case study of an existing building showing that the column removal situation is not always critical whereas the slab falling from above is much more detrimental.

Keywords: Punching, Flat slabs, Reliability analysis, Progressive collapse, Dynamic amplification factor, Finite element analysis, Column failure, Floor impact, Explosion load

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Modeling the Response of Concrete Slabs Under Blast Loading

Modeling the Response of Concrete Slabs Under Blast Loading

Pierluigi Olmati¹, Patrick Trasborg², Clay Naito³, Luca Sgambi⁴, Franco Bontempi⁵

Abstract

The structural response assessment of reinforced concrete slabs subjected to impulsive loads due to a detonation of an explosive is an essential task for the design of blast resistant concrete structures. Nonlinear dynamic finite element methods and analytical modeling provide a valuable tool for predicting the response and assessing the safety of a reinforced concrete component. The proposed Finite Element analysis and analytical modeling approaches were validated using a series of shock tube tests conducted on conventionally constructed and high strength reinforced concrete slabs by the University of Missouri Kansas City at the Engineering Research and Design Center, U.S. Army Corps of Engineers in Vicksburg, Mississippi. The aim of the paper is to present the modeling techniques adopted in both the Finite Element and analytical modeling approaches in order to conduct the structural response assessment of RC slabs subjected to impulsive loads due to detonations. The numerical modeling was conducted utilizing LS-Dyna^® finite element software package. The analytical approach utilized a fiber analysis method coupled with a single degree of freedom time stepping method. The constitutive models, loading and boundary conditions utilized are discussed in detail.

Keywords: Analytical Modeling; Blast Blind Prediction Contest 2012; Blast Engineering; Finite Element Analysis; Fiber Analysis; SDOF Analysis.

Pierluigi Olmati, Patrick Trasborg, Clay Naito, Luca Sgambi, and Franco Bontempi. Modeling The Response of Concrete Slabs Under Blast Loading. Journal of the American Concrete Institute, 2016, Vol. 306, pp. 5.1-5.20

1 P.E., Ph.D., Tokyo Polytechnic University, Atsugi, Kanagawa, Japan, Email: pierluigi.olmati@gmail.com

2 Graduate Student Researcher. Department of Civil and Env. Engr., Lehigh University ATLSS Center, 117 ATLSS Dr., Bethlehem, PA 18015, USA, Email: patrick.trasborg@gmail.com

3 Ph.D., P.E., Associate Professor. Department of Civil and Env. Engr., Lehigh University ATLSS Center, 117 ATLSS Dr., Bethlehem, PA 18015, USA, Email: cjn3@Lehigh.edu, Phone: 610-758-6229

4 P.E., Ph.D., Assistant Professor, Department of Civil and Environmental Engineering, Politecnico di Milano, Piazza L. da Vinci 32 20133 Milan (Italy), Email: luca.sgambi@polimi.it

5 P.E., Ph.D., Full Professor, Sapienza Università di Roma, School of Civil and Industrial Engineering, Via Eudossiana 18-00184 Rome (Italy), Email: franco.bontempi@uniroma1.it

 

Simplified fragility-based risk analysis for impulse governed blast loading scenarios

Simplified fragility-based risk analysis for impulse governed blast loading scenarios

Pierluigi Olmati a*, Francesco Petrini b, Dimitrios Vamvatsikos c, Charis Gantes c

a Tokyo Polytechnic University, Atsugi, Kanagawa, Japan
b Sapienza University of Rome, School of Civil and Industrial Engineering, Rome, Italy
c National Technical University of Athens, School of Civil Engineering, Athens, Greece
* Corresponding author.
E-mail address: pierluigi.olmati@gmail.com (P. Olmati).
http://dx.doi.org/10.1016/j.engstruct.2016.01.039

Abstract

Blast-loaded structures are presently assessed and designed following a deterministic approach, where only a set of structural analyses under worst-case design scenarios are carried out in order to verify each limit state. As a rational alternative, a conditional probabilistic approach is introduced to offer comprehensive risk assessment and to allow the design with user-defined confidence in meeting performance targets in view of uncertainties. To simplify the probabilistic consideration of the uncertain parameters, the determination of the blast hazard and the structural response are decoupled into the evaluation of blast hazard curves and structural fragilities curves, respectively, by introducing a single conditioning intensity measure. This is chosen to be the impulse density, shown to be sufficient for impulse governed scenarios, achieving a reduction of the computational effort by several orders of magnitude without introducing bias. Furthermore a problem-specific safety factor formulation is introduced to incorporate the influence of uncertainties in a simple manner, akin to current engineering practice. As a proof-of-concept test, a steel built-up blast resistant door is subjected to an accidental detonation of mortar rounds in a military facility. The equivalent single degree of freedom model is adopted in order to conduct the structural analyses, while detailed finite element analyses are carried out for validation. Finally, the conditional approach risk analysis on the steel door is compared against the results obtained through the comprehensive (probabilistic) unconditional approach, showing the validity of both the proposed intensity measure and safety factor formulation.

Keywords:

Performance-based design

Fragility analysis

Safety factor

Steel built-up blast resistant door

Simplified SDOF model

Monte Carlo simulation

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