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Anchorage in Concrete Structures: Numerical and Experimental Evaluations of Load-Carrying Capacity of Cast-in-Place Headed Anchors and Post-Installed Adhesive Anchors
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. (Division of Structural and Fire Engineering)ORCID iD: 0000-0001-9937-6072
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Various anchorage systems including both cast-in-place and post-installed anchors have been developed for fastening both non-structural and structural components to concrete structures. The need for increased flexibility in the design of new structures and strengthening of existing concrete structures has led to increased use of various metallic anchors in practice. Although millions of fasteners are used each year in the construction industry around the world, knowledge of the fastening technology remains poor. In a sustainable society, buildings and structures must, from time to time, be adjusted to meet new demands. Loads on structures must, in general, be increased to comply with new demands, and the structural components and the structural connections must also be upgraded. From the structural connection point of view, the adequacy of the current fastenings for the intended increased load must be determined, and inadequate fastenings must either be replaced or upgraded. The current design models are generally believed to be conservative, although the extent of this behavior is not very clear. To address these issues, the current models must be refined to allow the design of new fastenings and also the assessment of current anchorage systems in practice.

The research presented in this thesis consists of numerical and experimental studies of the load-carrying capacity of anchors in concrete structures. Two different types of anchors were studied: (I) cast-in-place headed anchors, and (II) post-installed adhesive anchors. This research focused particularly on the tensile load-carrying capacity of cast-in-place headed anchors and also on the sustained tension loading performance of post-installed adhesive anchors. The overall objective of this research was to provide knowledge for the development of improved methods of designing new fastening systems and assessing the current anchorage systems in practice.

For the cast-in-place headed anchors (I), the influence of various parameters including the size of anchor head, thickness of concrete member, amount of orthogonal surface reinforcement, presence of concrete cracks, concrete compressive strength, and addition of steel fibers to concrete were studied. Among these parameters, the influence of the anchor head size, member thickness, surface reinforcement, and cracked concrete was initially evaluated via numerical analysis of headed anchors at various embedment depths. Although these parameters have considerable influence on the anchorage capacity and performance, this influence is not explicitly considered by the current design models. The numerical results showed that the tensile breakout capacity of headed anchors increases with increasing member thickness and/or increasing size of the anchor head or the use of orthogonal surface reinforcement. However, their capacity decreased considerably in cracked concrete. Based on the numerical results, the current theoretical model for the tensile breakout capacity of headed anchors was extended by incorporating several modification factors that take the influence of the investigated parameters into account. In addition, a supplementary experimental study was performed to verify the numerically obtained findings and the proposed refined model. The experimental results corresponded closely to the numerical results, both in terms of failure load and failure pattern, thereby confirming the validity of the proposed model. The validity of the model was further confirmed through experimental results reported in the literature.

Additional experiments were performed to determine the influence of the concrete compressive strength and the addition of steel fiber to concrete on the anchorage capacity and performance. These experiments showed that the anchorage capacity and stiffness increase considerably with increasing concrete compressive strength, but the ductility of the anchor decreases. However, the anchorage capacity and ductility increased significantly with the addition of steel fibers to the concrete mixture. The test results also revealed that the tensile breakout capacity of headed anchors in steel fiber-reinforced concrete is significantly underestimated by the current design model.

The long-term performance and creep behavior of the post-installed headed anchors (II) was evaluated from the results of long-time tests on adhesive anchors under sustained loads. In this experimental study, adhesive anchors of various sizes were subjected to various sustained load levels for up to 28 years. The anchors were also exposed to several in-service conditions including indoor temperature, variations in the outdoor temperature and humidity, wetness (i.e., water on the surface of concrete), and the presence of salt (setting accelerant) additives in the concrete. Among the tested in-service conditions, variations in the outdoor temperature and humidity had the most adverse effect on the long-term sustained loading performance of the anchors. Based on the test results, recommendations were proposed for maximum sustained load levels under various conditions. The anchors tested under indoor conditions could carry sustained loads of up to 47% of their mean ultimate short-term capacities. However, compared with these anchors, the anchors tested under outdoor conditions exhibited larger creep deformation and failure occurred at sustained loads higher than 23% of their mean ultimate short-term capacities. Salt additives in concrete and wet conditions had negligible influence on the long-term performance of the anchors, although the wet condition resulted in progressive corrosion of the steel. Based on the experimental results, the suitability of the current testing and approval provisions for qualifying adhesive anchors subjected to long-term sustained tensile loads was evaluated. The evaluations revealed that the current approval provisions are not necessarily reliable for qualifying adhesive anchors for long-term sustained loading applications. Recommendations were given for modifying the current provisions to ensure safe long-term performance of adhesive anchors under sustained loads.

Place, publisher, year, edition, pages
Luleå- Sweden: Luleå University of Technology, 2017. , 352 p.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword [en]
Headed anchor; Anchor bolt; Adhesive anchor; Concrete cone breakout; Concrete splitting; Pullout loading; Size effect; Member thickness; Anchor head size; Orthogonal surface reinforcement; Concrete Strength; High-strength concrete; Cracked concrete; Steel fiber-reinforced concrete; Sustained loading; Creep behavior.
National Category
Civil Engineering
Research subject
Structural Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-66333ISBN: 978-91-7790-002-3 (print)ISBN: 978-91-7790-003-0 (electronic)OAI: oai:DiVA.org:ltu-66333DiVA: diva2:1153811
Public defence
2017-11-30, F1031, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2017-11-06 Created: 2017-10-31 Last updated: 2017-11-24Bibliographically approved
List of papers
1. Tensile capacity of anchor bolts in uncracked concrete: Influence of member thickness and anchor’s head size
Open this publication in new window or tab >>Tensile capacity of anchor bolts in uncracked concrete: Influence of member thickness and anchor’s head size
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2017 (English)In: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 114, no 6, 1517-1528 p.Article in journal (Refereed) In press
Abstract [en]

This study evaluated the influence of concrete member thickness and size of anchor head on the tensile capacity and performance of anchor bolts in concrete. Anchor bolts at various embedment depths (hef=50 – 500 mm (1.97 – 19.69 in.)) in concrete members of various thicknesses (H=1.5 – 5.0∙hef) were simulated. Three different sizes of anchor head (small, medium and large) were considered at each anchor embedment depth. The numerical results were compared with predictions from several theoretical and empirical models, including current design models, as well as some test results.

The numerical results show that the concrete cone resistance increases with increasing thickness of concrete member and/or size of the anchor head. Simulations also indicate that current design models generally underestimate the tensile capacity of large anchors.

Two modification factors are proposed to account for the influence of the member thickness and the size of anchor head. Predictions of anchorage capacity using the proposed modification factors have good correlation with the available test results found in the literature.

Place, publisher, year, edition, pages
American Concrete Institute, 2017
Keyword
anchor bolt; concrete cone breakout; pullout loading; size effect; member thickness; head size.
National Category
Civil Engineering Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-66330 (URN)
Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2017-11-24
2. Influence of Surface Reinforcement, Member thickness and Cracked Concrete on Tensile Capacity of Anchor Bolts
Open this publication in new window or tab >>Influence of Surface Reinforcement, Member thickness and Cracked Concrete on Tensile Capacity of Anchor Bolts
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2017 (English)In: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 114, no 6Article in journal (Refereed) In press
Abstract [en]

An extensive numerical study was carried out to evaluate the influence of concrete member thickness and orthogonal surface reinforcement on the tensile capacity and performance of anchor bolts in uncracked concrete members. Anchor bolts at various embedment depths (hef=50 to 300 mm (1.97 to 11.81 in.)) in unreinforced and reinforced concrete members of various thicknesses (H=1.5 – 5.0∙hef) were simulated. The reinforced concrete slabs were considered to be lightly-reinforced and over-reinforced to evaluate also the influence of amount of reinforcement. Furthermore, the behavior of anchor bolts at various embedment depths in pre-cracked reinforced concrete members was numerically investigated. The numerical results were compared with predictions from current design models including the Concrete Capacity (CC) method.

The numerical results show that in uncracked concrete the tensile capacity of anchor bolts increases up to 20% and the anchorage behavior becomes more ductile with increasing member thickness or by having surface reinforcement. The numerical results also show that the CC method underestimates the tensile capacity of deep anchors (hef≥200 mm (7.87 in.)), while it slightly overestimates the capacity of short anchors (hef≤100 mm (3.94 in.)) in thin unreinforced members. It was also found that the over-reinforced concrete does not improve the anchorage capacity and performance any further than the lightly-reinforced concrete. Based on the numerical results, several recommendations are proposed to account for the influence of member thickness, surface reinforcement and cracked concrete. Further experimental studies are ongoing to verify and generalize the recommendations of this study.

Place, publisher, year, edition, pages
American Concrete Institute, 2017
Keyword
headed anchor; cone breakout failure; splitting failure; tension loading; surface reinforcement; member thickness, cracked concrete.
National Category
Civil Engineering Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-66331 (URN)
Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2017-11-24
3. Experimental Evaluations of Influence of Member Thickness, Anchor-Head Size, and Reinforcement on the Tensile Capacity of Headed Anchors in Uncracked Concrete
Open this publication in new window or tab >>Experimental Evaluations of Influence of Member Thickness, Anchor-Head Size, and Reinforcement on the Tensile Capacity of Headed Anchors in Uncracked Concrete
2017 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541XArticle in journal (Refereed) In press
Abstract [en]

Cast-in-place headed anchors with different head sizes embedded in plain and reinforced concrete members of various thicknesses were subjected to pullout tests. The influence of member thickness, size of the anchor head, and orthogonal surface reinforcement on the tensile capacity and performance of anchor bolts was evaluated. The member thickness varied from 1.5 to 3.0 times the anchor embedment depth and headed anchors with small, medium, and large heads were tested.

The experimental results of the present study showed that increasing member thickness and/or the use of orthogonal surface reinforcement lead to increased anchorage capacity and anchorage ductility, whereas the anchorage stiffness decreases slightly. In contrast to the anchorage ductility, the tensile breakout resistance and the anchorage stiffness increase significantly with increasing size of the anchor head.

The experimental results corresponded closely to numerical results from a previous study (Nilforoush et al. 2016 a & b), which suggested a modified model incorporating several modification factors for improving the predictive capability of the Concrete Capacity (CC) method. In the present study, these factors yielded improved prediction of the tensile breakout capacity of the tested headed anchors.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2017
Keyword
headed anchor; anchor bolt; concrete cone breakout; concrete splitting; member thickness; anchor head; surface reinforcement.
National Category
Civil Engineering Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-66332 (URN)
Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2017-11-24
4. Experimental evaluation of tensile behaviour of single cast-in-place anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete
Open this publication in new window or tab >>Experimental evaluation of tensile behaviour of single cast-in-place anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete
2017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, 195-206 p.Article in journal (Refereed) Published
Abstract [en]

Cast-in-place anchor bolts embedded in plain and steel fibre-reinforced normal- and high-strength concrete members were subjected to monotonic tensile loads. The influence of the concrete member thickness, concrete strength, and the addition of steel fibres to the concrete mixture, on the anchorage capacity and performance was evaluated. The experimental results were evaluated in terms of anchorage capacity, anchorage ductility and stiffness as well as failure mode and geometry. Furthermore, the validity of Concrete Capacity (CC) method for predicting the tensile breakout capacity of anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete members was evaluated.

The anchorage capacity and ductility increased slightly with increasing member thickness, whereas the anchorage stiffness decreased slightly. In contrast to the anchorage ductility, the anchorage capacity and stiffness increased considerably with increasing concrete compressive strength. The anchorage capacity and ductility also increased significantly with the addition of steel fibres to the concrete mixtures. This enhanced capacity and ductility resulted from the improved flexural tensile strength and post-peak cracking behavior of steel fibre-reinforced concrete.

The average ratio of measured strengths to those predicted by the CC method for anchors in plain concrete members was increased from 1.0 to 1.17 with increasing member thickness. In steel fibre-reinforced concrete, this ratio varied from 1.29 to 1.51, depending on the member thickness and the concrete strength.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Anchor bolt; Headed anchor; Concrete cone breakout; Splitting failure; Normal-strength concrete; High-strength concrete; Member thickness; Steel fibre-reinforced concrete
National Category
Civil Engineering Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-63862 (URN)10.1016/j.engstruct.2017.05.062 (DOI)000408073500015 ()2-s2.0-85020246241 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-06-12 (andbra)

Available from: 2017-06-10 Created: 2017-06-10 Last updated: 2017-11-24Bibliographically approved
5. Long-Term Performance of Adhesive Bonded Anchors
Open this publication in new window or tab >>Long-Term Performance of Adhesive Bonded Anchors
2016 (English)In: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 113, no 2, 251-261 p., MS No. S-2014-302.R2Article in journal (Refereed) Published
Abstract [en]

Post-installed adhesive anchors used for fastening nonstructural and/or structural elements to concrete structures are prone to creep under sustained loads over their service life, which may considerably affect their long-term performance. In this study, the influence of various in-service conditions and sustained loading levels on the long-term performance of adhesive anchors was experimentally examined. The tested adhesive was an unsaturated polyester resin and the bonded anchors were subjected to sustained loads of 23, 47 and 70% of their mean ultimate short-term capacities for up to 10376 days (28.4 years). The tested in-service conditions were indoor temperature, outdoor temperature and humidity variations, wetness and presence in the concrete of salt additives.Results indicate that the tested bonded anchors did not fail indoors when subjected to sustained loads up to 47% of their mean ultimate short-time capacity. However, the long-term performance was substantially impaired outdoors, presumably due to temperature and humidity variations, leading to failure for sustained loads higher than 23% of the anchors’ mean ultimate short-time capacity.

Keyword
bonded anchor, adhesive anchor, anchorage, fastening, sustained load, creep behavior, Civil engineering and architecture - Building engineering, Samhällsbyggnadsteknik och arkitektur - Byggnadsteknik
National Category
Infrastructure Engineering
Research subject
Structural Engineering; Attractive built environment (AERI)
Identifiers
urn:nbn:se:ltu:diva-10694 (URN)10.14359/51688060 (DOI)000388213000006 ()9889f521-1abc-4490-b85d-eaf0dea6e2cd (Local ID)9889f521-1abc-4490-b85d-eaf0dea6e2cd (Archive number)9889f521-1abc-4490-b85d-eaf0dea6e2cd (OAI)
Note

Validerad; 2016; Nivå 2; 20160201 (rasnil)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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