Shearing of rock joints is a critical failure mode in rock masses. The shear strength of rock joints must, therefore, be considered in the design of structures in rock masses. Several criteria for prediction of shear strength have been proposed over the years. However, the possible effect of scale on shear strength is an issue. One possible reason for this is that previous experimental studies on the scale effect contain various sources of uncertainties (mixed test methods, multiple testing of same specimen, application of results to other materials than tested, and omitted handling of statistical dispersion). In this paper, the results from a uniquely comprehensive experimental laboratory program, that handles these uncertainties and also extends the range of previously tested conditions, is presented. 46 direct shear tests on two joint types, natural and tensile induced granite rock joints, have been performed under the constant normal stress and the constant normal stiffness boundary condition at 5 MPa initial normal stress applied over three specimen sizes (35 mm × 60 mm, 70 mm × 100 mm and 300 mm × 500 mm). Analysis of variance shows no effect of the specimen size on the shear strength, whereas the joint type and boundary condition has. Quantitative estimates of the influence of the joint type and boundary condition on the shear strength are presented. A consistent approach for determination of shear strength from the point of time associated with a shear stiffness change of the test system is also presented

Prestressed concrete offers a range of benefits compared to traditional reinforced concrete, but in some markets the application of post-tensioned structures has seen a decline in recent decades. A critical aspect of post-tensioned structures is the design of anchorage zones. This study introduces and evaluates an experimental method based on Distributed Optical Fibre Sensors (DOFS) to assess the behaviour of post-tensioned anchorage zones. Moreover, the effectiveness of steel fibre reinforced concrete (SFRC) is also compared to various setups using conventional reinforcement systems. The aspects analysed include load-deformation behaviour, initial crack formation, and subsequent crack development. The research, based on six tested samples, shows that the application of DOFS in the presented setup holds great potential. Furthermore, the findings indicate that using exclusively SFRC at a volume fraction of 0.5%, without passive reinforcement is not recommended. However, combining SFRC with standard helical reinforcement around the anchorage block appears sufficient to meet desired structural performance, as evidenced by comparisons to control specimens. 

Reinforced concrete (RC) protective structures require a large energy absorption capacity if they are to effectively withstand impulse loading due to blast or impact. Such structures may be subjected to both single and repeated impulse loading but there are just a few studies for the latter case. Therefore, in this study, experiments were conducted on RC beams, which were subjected to single or repeated drop-weight impacts. The beam response during impact was studied using a high-speed camera and digital image correlation. To determine the total energy absorption capacity, the impact-loaded beams were subjected to static loading until failure and the results compared to those of statically loaded reference beams. The total energy absorption capacity was of the same order or higher for beams previously subjected to impact loading, with a strong impact resulting in a greater increase. For tests in which the total impact energy was kept constant, repeated impact loading caused increased local damage, whilst decreasing the total energy absorption capacity.

This paper presents an experimental and numerical investigation on the structural response of stainless steel trapezoidally corrugated web girders subjected to patch loading. Four girders were tested to failure, the length and position of the patch load within the corrugation profile were varied to investigate its impact on the ultimate load and failure modes. All four girders were made of lean duplex stainless steel (EN 1.4162/LDX 2101). Initial geometric imperfections were measured using a digital image correlation system. The load-displacement responses and the failure modes were analyzed in detail. In addition, geometrically and materially nonlinear analyses with imperfection included (GMNIA) were also performed. Measured initial imperfections were included in the model. The numerical model was verified against the experimental results. Stress distribution plots were also obtained numerically to further analyze the failure modes and the influence of the strain hardening capacity of stainless steel. Ultimate loads obtained experimentally were also compared with predicted resistances using theoretical models available in the literature. According to the results, neglecting the flange resistance to patch loads according to standard EC3:1–5 leads to a significant underestimation of the capacity of stainless steel and carbon steel corrugated web girders. However, considering the resistance from both the flange and web, the difference between the design model and test results is limited to a safe range of 3–12 % for all four tested girders.

The response of masonry structures to impacts is a topic of significant importance due to its implications in structural integrity and safety. In this paper, the impulsive response of unreinforced brick masonry walls to impacts was investigated through a series of laboratory pendulum tests. Four double-wythe clay brick masonry wall strips were constructed between reinforced concrete slabs and subjected to moderate-velocity impacts. The tests included both point-load and line-load impacts, with a non-rigid support condition for the upper wall support to simulate realistic axial load applications. Measurements included: load cells monitoring the axial load applied to the top of the walls, capturing the arching generated upon impact; high-speed cameras used in conjunction with 3D DIC, to monitor strain rates and crack evolution on the wall surface; and 3D LiDAR scans, to support the documentation of post-test observed damage. The findings offered a comprehensive and detailed analysis of the structural response of brick masonry walls subjected to impacts. By focusing on specific response metrics, the study elucidated the various failure mechanisms generated by the impacts. Additionally, the energy transferred during the impacts was quantified, providing a direct measure of the energy absorption capacity of the walls and its correlation with the observed failures.

Outer walls are a crucial component of the building envelope, providing insulation and structural support. While they are originally designed to support axial loads, these walls can be subjected to extreme loads, like the ones generated by impacts and blasts. Unreinforced brick masonry walls are particularly vulnerable to these actions and pose significant risks when damaged, including flying debris and progressive collapse. Careful engineering judgment is required to evaluate their resistance and design their strengthening in order to address this problem. A 3D FEM-based meso-scale modelling strategy is developed to simulate the response of masonry walls to blasts and impacts. The models were created in a general-purpose proprietary FEA software package, by making use of material models available in it. Bricks were modelled as nonlinear solid elements, while mortar joints were modelled by contact interfaces with cohesive-damage frictional behaviour. The models were built and verified upon the findings of impact pendulum and quasi-static four-point bending tests, both conducted at RISE Research Institutes of Sweden under various wall configurations. Once validated, the ability of this modelling strategy to conduct blast simulations was demonstrated for one of the tested wall configurations. This numerical work complements the experimental work previously conducted at RISE to characterize the response of brick masonry walls under impulsive loads. The modelling strategy presented here can assist the analyst evaluate the resistance of brick facades to these loads, allowing for a more precise assessment of urban areas at risk of damage.

Wedge splitting tests were conducted on a granite and a gneiss with similar mineralogy but different microstructure. The basic properties of the two rock types were characterized by petrographic analy- ses and mechanical tests. The granite specimens were split in one material direction, perpendicular to the rift plane, and the gneiss specimens were split in three dif- ferent material directions, parallel and perpendicular to the foliation (and along and across a lineation). The effect of having a large blunt versus a sharp notch on the crack initiation was studied in the granite. The wedge splitting tests are unconventional for testing rocks and allowed to study the crack initiation and propagation under mode I loading condition in the quasi-brittle granite and brittle gneiss. The fracture energy and strain energy release rate were calculated. The strain energy release rate for gneiss, when splitting along and across the foliation, was around 45% and 60% of the values for the structurally isotropic granite. The fracture toughness was calculated from the strain energy release rate and was larger than corresponding values obtained from linear elastic fracture mechanics (LEFM). There was an effect on the early cracking stages by using a sharp notch compared with using a large blunt notch on the granite specimens, but the required largest force to split the specimens remained the same for the two notch types. The crack initiation started at a splitting force corresponding to 78% and 90% of the maximum splitting force on the specimens with a sharp notch and a large blunt notch, respectively. The results with a full force-displacement response during the crack propagation obtained for the brittle gneiss are unique. Most fracture mechanics results on rock materials are obtained from standard tests and LEFM and not via the measured strain energy release rate.

The development of an innovative rock anchor prototype manufactured using high strength steel sheets produced locally in Sweden is the core of the PROWIND concept. Steel sheets provide a design freedom to easily manufacture complex geometries, which can be advantageous to enhance the shear force transmission in the bond-length segment of the anchor. The underlying challenge of this concept has been to design a solution which meets the design requirements of today and future technological advancements, all while keeping conventional installation practices in mind. The project followed a 4-step development process: (1) concept analysis and modelling, (2) small-scale prototypes testing and (3) large scale lab-validation and lastly (4) field validation. The performance of the developed rock anchor prototype and grouting material was experimentally quantified on both small and large-scale test specimens and also validated in full scale in the field concerning installation process, proof-loading and maintaining the prestress over time. The PROWIND anchors with the end feature with ribbed design have 4-5 times higher load bearing capacity. The experience from the anchor installation proved that the developed grout and anchors are faster and easier to install. The field test in two different geological conditions has proven that the news design is reducing the required anchorage length to just 1 meter. The restressing of anchors is fully possible with the proposed lock-off solution with a nut. All of those contribute to lower costs of installations and possibly longer service-life.

Prestressed concrete structures have numerous advantages over conventionally reinforced concrete, though the usage of post-tensioned structures has declined over the last two decades.An essential design detail in post-tensioned structures is the anchorage zones.In this study an experimental comparison is presented for post-tensioned anchorage zones.The study evaluates the load-deformation response and cracking of three different configurations.In total, six specimens are tested experimentally by subjecting them to centric loading until clear crack formations were observed.The evaluation and comparison of the three different configurations are done by comparing the data obtained from the tests.The results presented in this paper are expected to provide further knowledge to develop and improve the contemporary design approach and construction of bridges

Experimentella undersökningar av skjuvegenskaperna hos bergsprickor i hårt berg har generellt fokuserat på mindre sprickprover för normalspänningar på upp till 20 MPa, representativa för ett kärnbränsleförvar på ca 400 meters djup. Vid stora sprickprover har skjuvegenskaperna generellt bestämts för låga spänningar, på någon eller några MPa. För att få en förståelse för inverkan av sprickornas storlek för skjuvegenskaperna vid höga normalspänningar är det avgörande att genomföra skjuvförsök på stora bergsprickor (> 200 mm) i hårt berg under höga normalspänningar. I projektet Parameterization of Fractures, POST (2014–2016), studerades skaleffekterna genom in situ-försök, småskaliga skjuvförsök och beräkningssimuleringar. Det konstaterades att laboratorieexperiment under kontrollerade förhållanden och på stora bergprover är nödvändiga för att få tillförlitliga resultat. Det konstaterades också att in-situ-försök är komplexa med stora underliggande osäkerheter och är samtidigt kostsamma. I det pågående projektet POST 2 som startade 2017 har bergsprickor på upp till 500 mm provats i en ny unik laboratorieutrustning, jämte provning av mindre sprickor, vid höga normalspänningar för både CNL och CNS förhållanden och med ny mätteknik. Teknik för att tillverka replikaprover av bergsprickor har utvecklats och provats med syfte att göra lastparameterstudier. Kvaliteten hos geometriavbildningen hos replikaproverna och sprickornas geometrier har uppmätts med högupplöst skanning. I denna artikel presenteras en del av resultaten från projektet. Resultaten från projektet är tillämpbara för andra områden med undermarkskonstruktioner såsom projektering av tunnlar och bergrum för infrastrukturprojekt och gruvor.

Experimental investigations of the shear properties of rock fractures in hard rock have generally focused on tests on smaller fracture s for normal stresses of up to 20 MPa, representative of a nuclear waste repository at a depth of about 400 meters. T he shear properties of large fractures determined at experiments have generally been determined at low stresses , of one or more MPa. To gain an understanding of the effect of the size on the shear properties of the fractures at high normal stresses, it is crucial to perform shear experiments on large rock fractures (> 200 mm) in hard rock under high normal stresses. In the project Parameterization of Fractures, POST (2014 2016), the scale effects were studied by in situ experiments, small scale shear experiments and computational simulations. It was found that laboratory experiments under controlled conditions and on large rock samples are necessary to obtain reliable results. It was also found that in situ experiments are complex with large underlying uncertainties and are at the same time costly. In the ongoing POST 2 project, which started in 2017, rock fractures up to 500 mm have been tested in a new unique laboratory equipment, along with test s on smaller fractures , at high normal stress for both CNL and CNS conditions and with new measurement technology. Techniques for producing replica samples of rock fractures have been developed and tested with the aim of making load parameter studies. The quality of the geometry imaging of the replica samples and the geometries of the fractures has been meas ured by high resolution scanning. This article presents some of the results from the project. The results from the project are applicable to other areas with underground construction, such as the design of tunnels and rock caverns for infrastructure projects and mines.