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Structural concrete elements subjected to air blast loading
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

In the design of structures to resist the effects of air blast loading or other severe dynamic loads it is vital to have large energy absorbing capabilities, and structural elements with large plastic deformation capacities are therefore desirable. Structures need to be designed for ductile response in order to prevent partial or total collapse due to locally failed elements. The research in this thesis considers experimental and theoretical studies on concrete beams of varying concrete strength. The nominal concrete compressive strength varied between 30 MPa and 200 MPa. A total of 89 beams were tested of which 49 beams were reinforced with varying amounts of tensile reinforcement. These beams were also reinforced with stirrups and steel fibres were added to a few beams. The remaining 40 beams were only reinforced with steel fibres with a fibre content of 1.0 percent by volume. Two different fibre lengths having constant length-to-diameter ratio were employed. The tests consisted of both static and air blast tests on simply supported beams. The blast tests were performed within a shock tube with a detonating explosive charge. All experimental research focused on deflection events, failure modes and loads transferred to the supports. The dynamic analyses involve single-degree-of-freedom (SDOF) modelling of the beam response and the use of iso-damage curves. Also, the dynamic support reactions were calculated and compared with test results.

For beams with tensile reinforcement, the failure mode of some beam types was observed to change from a flexural failure in the static tests to a flexural shear failure in the dynamic tests. Beams with a high ratio of reinforcement and not containing steel fibres failed in shear, whereas beams with a lower ratio of reinforcement failed in flexure. The introduction of steel fibres prevented shear cracks to develop, thus increasing the shear strength of the beams. The presence of steel fibres also increased the ductility and the residual load capacity of the beams. Beams subjected to air blast loading obtained an increased load capacity when compared to the corresponding beams subjected to static loading. The SDOF analyses showed good agreement with the experimental results regardless of concrete strength and reinforcement amount. The results of using iso-damage curves indicate conservative results with larger load capacities of the beams than expected. The theoretical evaluations of the dynamic reactions were in agreement with the measured average reactions, both in amplitudes and in general shape.

The experimental results with steel fibre reinforced concrete beams indicate that the dynamic strength was higher than the corresponding static strength and that the toughness was reduced when increasing the compressive strength. Beams of normal strength concrete failed by fibre pull-out while a few beams of high strength concrete partly failed by fibre ruptures. It may be favourable to use shorter fibres with smaller aspect ratios in structural elements of high strength concrete and subjected to large dynamic loads.

Further research should involve studies on the size effect, on different boundary conditions, on different types of structural elements and on the combination of blast and fragment loads. The theoretical work should involve analyses both with the use of SDOF modelling and finite element analysis.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , xii, 82 p.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 92
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-4441OAI: oai:DiVA.org:kth-4441DiVA: diva2:12322
Presentation
2007-06-11, Seminarierummet, Byggvetenskap, KTH, Brinellvägen 34, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101112Available from: 2007-06-18 Created: 2007-06-18 Last updated: 2012-02-13Bibliographically approved
List of papers
1. High strength concrete beams subjected to shock waves from air blast
Open this publication in new window or tab >>High strength concrete beams subjected to shock waves from air blast
2002 (English)In: Proceedings of the 6th International Symposium on Utilization of high strength/high Performance Concrete, 355-368 p.Article in journal (Refereed) Published
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-7335 (URN)
Note
QC 20101112Available from: 2007-06-18 Created: 2007-06-18 Last updated: 2012-01-23Bibliographically approved
2. Reinforced high strength concrete beams subjected to air blast loading
Open this publication in new window or tab >>Reinforced high strength concrete beams subjected to air blast loading
2004 (English)In: STRUCTURES UNDER SHOCK AND IMPACT VIII, ASHURST, ENGLAND: WIT PRESS , 2004, 53-62 p.Conference paper, Published paper (Refereed)
Abstract [en]

A total of 49 reinforced concrete beams of both high strength concrete (HSC) and, for reference, normal strength concrete (NSC) were tested. 38 beams were subjected to air blast loading in a shock tube and the remaining eleven beams were tested statically for reference. Concrete with nominal compressive cube strengths 40, 100, 140, 150 and 200 MPa were used and a few beams also contained steel fibres. Furthermore, beams with two concrete layers of different strength were tested. The purpose of this investigation was to study the structural behaviour of the concrete beams subjected to air blast loading.

All beams subjected to static loading failed in flexure. In the dynamic tests, beams without fibres and with high ratios of reinforcement exhibited shear failure. It was observed that the inclusion of steel fibres in the matrix increased the shear strength and the ductility of the beams. This investigation indicates that beams subjected to air blast loading obtained an increased load capacity when compared to the corresponding beams subjected to static loading.

Place, publisher, year, edition, pages
ASHURST, ENGLAND: WIT PRESS, 2004
Series
STRUCTURES AND MATERIALS, ISSN 1462-6055 ; 15
Keyword
air blast loading, high strength concrete, steel fibres, reinforcement, failure modes
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-7336 (URN)000223144500006 ()1-85312-706-X (ISBN)
Conference
8th International Conference on Structures Under Shock and Impact Iraklion, GREECE, MAR, 2004
Note
QC 20101112Available from: 2007-06-18 Created: 2007-06-18 Last updated: 2012-02-13Bibliographically approved
3. Fibre reinforced concrete beams subjected to air blast loading
Open this publication in new window or tab >>Fibre reinforced concrete beams subjected to air blast loading
2006 (English)In: Nordic Concrete Research, ISSN 0800-6377, no 35, 18-34 p.Article in journal (Refereed) Published
Abstract [en]

This paper involves testing of steel fibre reinforced concrete(SFRC) beams subjected to static and dynamic loads. Thedynamic load was generated by a detonating explosive charge.The work focused upon studying the mechanical behaviour ofthe beams. The concrete compressive strength varied between36 MPa and 189 MPa with a fibre content of 1.0 percent byvolume. Two different fibre lengths having constant length-todiameterratio were employed. The experimental results indicatethat the toughness is reduced when increasing the compressivestrength and the dynamic strength is higher than thecorresponding static strength.

Keyword
steel fibres, high strength concrete, air blast loading, toughness
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-7337 (URN)
Note

QC 20101112

Available from: 2007-06-18 Created: 2007-06-18 Last updated: 2017-12-14Bibliographically approved

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