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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