<p>Structural walls in existing buildings designed to pre 1970s codes may have deficient shear reinforcement and lap splice detailing. Lap splices at the bottom of the walls were designed in compression with anchorage length of 24-bar diameter. When the structural wall is subjected to lateral loads during a major seismic event, the lap splice is in the zone of maximum moment and shear and may be subjected to tension. Such design may cause nonductile behaviour and sudden failure of the wall due to shear or bond slip of the lap splice reinforcing bars. The effect of shear and ductility rehabilitation on the behaviour of reinforced concrete structural walls, without lap splice, have shown improvement in the structural wall shear resistance and ductility and hence overall structural ductility and seismic loads resistance. Research on rehabilitation of reinforced concrete (RC) structural walls with both deficient shear reinforcement and lap splice detailing is still needed. </p> <p> The principal objectives of this study were to evaluate the seismic behaviour of non-ductile reinforced concrete structural walls before and after rehabilitation using carbon fibre reinforced polymers (CFRP). These objectives were achieved through experimental and analytical investigations.</p> <p> The experimental phase of this research involved testing large scale models of RC structural walls with deficient shear strength and lap splice detailing to reproduce failure modes observed following major seismic events and to evaluate the rehabilitation schemes. Ten RC structural walls were built and tested under cyclic loading. Three control walls were tested as-built with non-ductile detailing and seven walls were rehabilitated before testing. The purpose of the rehabilitation techniques was to prevent brittle failure in shear or bond slip and to improve the ductility and energy dissipation of RC structural walls.</p> <p> The analytical phase of this study involved evaluation of the inelastic dynamic response of RC residential building with nonductile structural walls as well as retrofitted walls. An efficient macroscopic model to represent the behaviour of RC structural walls when subjected to pushover, cyclic and dynamic seismic loads was developed. The proposed model was intended to adequately describe the hysteretic behaviour of walls and to be capable of accurately predicting both flexural and shear components of inelastic deformation. The model predictions were compared with the experimental results. The comparisons showed that the developed analytical model predicted the inelastic walls response with a good accuracy. The analytical model was capable to evaluate the nonlinear dynamic behaviour of an existing building under seismic excitation before and after rehabilitation.</p> / Thesis / Doctor of Philosophy (PhD)

Yes / Test results of 24 reinforced concrete continuous deep beams are reported. The main variables studied were concrete strength, shear span-to-overall depth ratio (a/h) and the amount and configuration of shear reinforcement. The results of this study show that the load transfer capacity of shear reinforcement was much more prominent in continuous deep beams than in simply supported deep beams. For beams having an a/ h of 0.5, horizontal shear reinforcement was always more effective than vertical shear reinforcement. The ratio of the load capacity measured and that predicted by the strutand-tie model recommended by ACI 318-05 dropped against the increase of a/h. This decrease rate was more remarkable in continuous deep beams than that in simple deep beams. The strut-and-tie model recommended by ACI 318-05 overestimated the strength of continuous deep beams having a/ h more than 1.0.

Reinforced concrete slab-column structures are widely used because of their practicality. However, this type of structures can be subject to punching-shear failure in the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subject to lateral loading in seismic zones. The shear bolts are a new type of transverse reinforcement developed for retrofit of existing structures against punching. This research focuses on how the shear bolts can improve the punching-shear capacity and ductility of the existing slab-column connections under vertical service and lateral seismic loads. A set of nine full-scale reinforced concrete slab-column connection specimens were tested under vertical service and cyclic loads. The vertical (gravity) load for each specimen was kept at a constant value throughout the testing. The cyclic lateral drift with increasing intensity was applied to the columns. The specimens were different in number of bolts, concrete strength, number of openings, and level of gravity punching load. Strains in flexural rebars in the slabs, crack widths, lateral loads, and displacements were obtained. The peak lateral load (moment) and its corresponding drift ratio, connection stiffness, crack width, and ductility were compared among different specimens. The testing results show that shear bolts can increase lateral peak load resisting capacity, lateral drift capacity at peak load, and ductility of the slab-column connections. Shear bolts also change the failure mode of the slab-column connections and increase the energy dissipation capacity. The thesis includes also research on the development of guidelines for shear bolt design for concrete slab retrofitting, including the punching shear design method of concrete slab (with shear bolts), dimensions of bolts, spacing, and influence of bolt layout patterns. Suggestions are given for construction of retrofitting method using shear bolts. Recommendations are also presented for future research.

Reinforced concrete slab-column structures are widely used because of their practicality. However, this type of structures can be subject to punching-shear failure in the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subject to lateral loading in seismic zones. The shear bolts are a new type of transverse reinforcement developed for retrofit of existing structures against punching. This research focuses on how the shear bolts can improve the punching-shear capacity and ductility of the existing slab-column connections under vertical service and lateral seismic loads. A set of nine full-scale reinforced concrete slab-column connection specimens were tested under vertical service and cyclic loads. The vertical (gravity) load for each specimen was kept at a constant value throughout the testing. The cyclic lateral drift with increasing intensity was applied to the columns. The specimens were different in number of bolts, concrete strength, number of openings, and level of gravity punching load. Strains in flexural rebars in the slabs, crack widths, lateral loads, and displacements were obtained. The peak lateral load (moment) and its corresponding drift ratio, connection stiffness, crack width, and ductility were compared among different specimens. The testing results show that shear bolts can increase lateral peak load resisting capacity, lateral drift capacity at peak load, and ductility of the slab-column connections. Shear bolts also change the failure mode of the slab-column connections and increase the energy dissipation capacity. The thesis includes also research on the development of guidelines for shear bolt design for concrete slab retrofitting, including the punching shear design method of concrete slab (with shear bolts), dimensions of bolts, spacing, and influence of bolt layout patterns. Suggestions are given for construction of retrofitting method using shear bolts. Recommendations are also presented for future research.

Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

The use of flat slabs in constructions due to its many functional and economic advantages is wide-spread. Behavior of flat slabs in shear and flexure is a fairly complex problem. Therefore, the punching shear failure belongs to one of the most critical aspects in the design of concrete buildings. Over the last decades several buildings have collapsed due to the failure of the punching shear strength, resulting in loss of lives and financial damages. These disasters revealed gaps in the current (or former) design codes and recommendations. As a part of theoretical framework of the dissertation a method for predicting the punching shear strength of flat slabs was developed. Several experiments on scaled down slabs were conducted in order to verify the proposed method and for optimization of its parameters. Proposed method in development predicts the punching shear for slabs without shear reinforcement according to the EC2 and replaces the area of the shear crack with a system of struts and ties.

Standards and regulations for dimensioning of load-bearing structures are based on the response of load-bearing structures subjected to loads without variation in time. In the event of an accidental load, e.g. a collision or explosion, causes the load to have a rapid variation in the time resulting in a dynamic response. Previous studies have shown that structures that respond in a certain way under static load have shown a completely different behavior under dynamic influence and therefore it is of interest to study the dynamic response of structures.By testing concrete beams with varying amounts of shear reinforcement subjected to impact loading, the purpose of this report is to analyze how the beams responds in terms of crack width and vibrations when they are exposed to a dynamic load. For comparison, reference tests have also been performed on beams subjected to a quasi-static load.The result of the project shows that the shear reinforcement comes into play as the beams with a larger amount of reinforcement have more capacity to hold the flexural shear cracks together. There is also an indication that the dynamic flexural shear capacity could be lower than static shear capacity as the shear cracks had an increased inclination during dynamic loading for some of the beams. This results in a decreased flexural shear capacity as only one stirrup carried the load across the shear crack.Measured signal shows that beams failing respond when impacted by the similar to a plastic collision, while beams responding with a flexure dominated mode without going to failure instead answer similar to an elastic collision. Furthermore, there is indication that the natural frequencies change significantly due to both flexural cracks and flexural shear cracks.

Impulsive loads have been observed to cause brittle shear failure in reinforced concrete elements designed for ductile failure modes under static loads. Brittle failure modes exhibit poorer energy absorption capabilities compared to ductile flexural failure modes due to their limited deformation capacity, leading to premature failure. The discrepancy between the responses under static and extreme dynamic loads arises from inertia and wave propagation effects, which tend to increase as the load duration decreases relative to the fundamental period of the element.   This thesis investigated the occurrence of shear failures in reinforced concrete elements subjected to impulsive loads, both experimentally and numerically, and evaluated to what extent current analysis methods for impulse-loaded structures can predict shear failure. Furthermore, the study examined the influence of crucial parameters on the energy absorption capacity during flexural failure modes when shear failure was inhibited.   The results demonstrated that shear-plug damage, prevalent during impact loads, may lead to premature shear failure during sequential impact testing. This occurred for a statically flexure-critical beam with a significantly larger static flexural-shear capacity relative to its flexural capacity. Similar conclusions applied to the residual static capacity after an initial impact introduced shear-plug damage. These findings indicate potentially severe consequences of shear-plug damage, which should be considered when assessing structures damaged by impact loads.   The energy absorption capacity of reinforced concrete elements is closely related to the plastic work capacity of the reinforcement. The experimental study showed how the plastic work capacity varied with reinforcement properties, concrete properties, and impact velocity using static and dynamic four-point flexural tests. The results revealed that the reinforcement type, specifically whether the steel is mild or stiff, governs the strain distribution during static and low-velocity impact testing. Generally, stiff steels result in strain localization before rupturing, indicating a lower plastic work capacity. Factors such as stress and strain capacity also proved significant. However, as the impact velocity increased, wave propagation effects governed strain distribution rather than reinforcement type.    Numerical studies comparing results with outcomes using proposed design methods indicated agreement for support reactions used to verify the shear capacity in the later stages of the response. However, this agreement decreased in the initial stages of the response. This may be because the dynamic equilibrium method only considers a global response, while the local response due to wave propagation is influential in the initial stages of the response. Today, resources such as Biggs [8] and the Swedish Fortifications Agency [86] recommend using two stages of the response to determine the internal forces; an elastic global response and a later elastoplastic global response. From the observations in the papers, it is suggested to add a third initial stage of the response considering wave propagation effects. However, it is deemed that this response stage only has a significant effect for high-intensity blast loads with short rise times relative to the shear wave velocity. / Impulsiva laster har i litteraturen visats leda till spröda skjuvbrott for armerade betongelement designade for mjuka brott under statiska laster. Spröda brottmoder påvisar sämre energiupptagande förmågor jämfört med mjuka böjbrott på grund av dess lägre deformationskapacitet, vilket resulterar i tidigt brott. Skillnaden i respons under statisk och dynamisk belastning kommer från tröghetskrafter och vågutbredningseffekter, där effekten av båda ökar med en minskande lastvaraktighet i relation till fundamentala perioden av elementet.   Det här arbetet undersöker förekomsten av skjuvbrott under impulsiva laster experimentellt och med numeriska analyser. Hur väl befintliga beräkningsmetoder kan förutspå skjuvbrott utvärderas aven. Dessutom studeras effekten av viktiga parametrar på den energiupptagande förmågan när skjuvbrott hämmas.   Resultaten påvisade att skjuv-plugg-skada, allmänt förekommande under stötbelastning, kan leda till tidigt skjuvbrott under sekventiell stötbelastning. Detta förekom for en statiskt böj-kritisk balk med en markant högre skjuvkapacitet relativt till dess böjkapacitet. Liknande slutsatser kunde dras vid provning av den statiska residualhållfastheten efter att ett initiellt fallviktsförsök introducerade skjuv-plugg-skada. Dessa resultat indikerar potentiellt allvarliga konsekvenser av skjuv-plugg-skada, vilket bör beaktas vid bedömning av element skadade från stötbelastning.   Den energiupptagande förmågan hos armerade betongelement är nära relaterat till det plastiska arbetet som armeringen kan utföra. Den experimentella studien visade hur kapaciteten for plastiskt arbete hos armeringen berodde på armeringsegenskaperna, betongegenskaperna samt anslagshastigheten hos massan vid statisk och dynamisk fyrpunktsbelastning. Resultaten visade att armeringstypen, mer specifikt ifall stålet var mjukt eller styvt, styrde töjningslokaliseringen under statisk belastning samt dynamisk belastning med låg anslagshastighet. Generellt sett resulterade styvare stål i töjningslokalisering när stålet slets av, vilket ledde till en mindre kapacitet for plastiskt arbete hos armeringsstången. Faktorer som töjnings- och spänningskapaciteten visades även vara betydande. Däremot indikerade resultaten att allt eftersom anslagshastigheten ökade så var vågutbredningseffekter det som bestämde grad av töjningslokalisering, och inte styvheten hos stålet.   Numeriska studier där resultat jämfördes mot resultat från rekommenderade designmetoder indikerade överenskommelse för stödreaktioner som används för att verifiera skjuvkapaciteten i ett senare skede av responsen. Däremot så var överenskommelsen sämre i ett tidigare skede av responsen. Detta kan möjligen förklaras av att den dynamiska jämviktsmodellen endast tar hänsyn till den globala responsen, medans lokal respons från vågutbredning är dominerande tidigt. Idag använder referenser som Biggs [8] och Fortifikationsverket [86] två stadium av responsen for att bestämma interna krafter; ett globalt elastiskt stadie och ett globalt elasiskt-plastiskt stadie. Från observationer i artiklarna så rekommenderas det att ett tredje initiellt stadie som beaktar vågutbredningseffekter bör inkluderas. Detta stadie anses dock bara visa markant effekt for intensiva stötvågsbelastningar med kort stegtid relativt till skjuvvågshastigheten i materialet. / <p>QC 230828</p>

Yes / The test results on eight two-span deep beams made of self-compacting concrete (SCC) are presented and discussed in this paper. The main parameters investigated were the shear span-to-depth ratio, and the amount and configuration of steel reinforcement. All beams failed due to a major diagonal crack formed between the applied mid-span load and the intermediate support separating the beam into two blocks: the first one rotated around the end support leaving the other block resting on the other two supports. Both concrete compressive strength and web reinforcement had a major effect in controlling the shear capacity of the beams tested. For the shear span-to-depth ratio considered, the vertical web reinforcement had more influence on the shear capacity of the specimens than the horizontal web reinforcement. The shear provisions of the ACI 318M-11 are unconservative for most of the beams tested. Comparisons of test results with the strut-and-tie model (STM) suggested by ACI 318M-11, EC2 and CSA23.4-04 showed that the predictions are reasonable for continuous deep beams made with low and medium compressive strength. Although the equation suggested by ACI 318M-11 is very simple, its prediction is more accurate than the STM suggested by different design codes. / This research investigation was funded by the Higher Education Ministry in The Libyan Government.

In this thesis the experimental results of seven full-scale glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) slab-column edge connections are presented. The dimensions of the slabs were 2,800×1,550×200 mm with a square column measuring 300×300×2,200 mm. The test connections were divided into two series. Series I included three connections investigating the effect of flexural reinforcement ratio (0.90, 1.35 and 1.80%) when high strength concrete (HSC) is used, while Series II included four connections investigating the effect of GFRP shear reinforcement type and pattern on normal strength concrete (NSC) connections. Test results showed that increasing the reinforcement ratio increased the punching capacity and the post-cracking stiffness of the HSC connections. Furthermore, the use of headed studs and corrugated bars increased the punching capacity and the deformability of the NSC connections. Test results were compared to the predictions of the Canadian and American design provisions for FRP-RC structures. / February 2017