京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第21042号 / 人健博第58号 / 新制||人健||4(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 坪山 直生, 教授 黒木 裕士, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

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>

This thesis investigates the in-plane shear performance of full-scale walls made from compressed earth blocks. Compressed earth blocks are a type of masonry where the blocks are composed of compressed soil and typically dry-stacked without mortar. Prior research has demonstrated that the in-plane shear strength of these blocks falls far short of capacities predicted by conventional masonry building codes, requiring new testing to develop effective and safe designs for seismic conditions. This thesis specifically studies the effects of block type and the use of grouted shear keys at the block head joints. Three full-scale walls were constructed and tested under in-plane, cyclic loading. To compare the effect of block type on shear strength, one wall was constructed from Rhino blocks as used by the Center for Vocational Building Technology, while another used V-Lock blocks designed by the Vermeer Corporation. Apart from differences in size and interlock mechanism, the standard Rhino blocks have shear keys at the head joints which are not present on the V-Lock blocks. To examine the effect of these shear keys, a third wall was built from Rhino blocks with the shear keys removed. The two standard block types displayed no major difference in strength that could not be attributed to grouted area or the presence/absence of the head joint shear keys. The Rhino block wall with shear keys reached a higher peak load relative to the grouted area but experienced a brittle drop in capacity after peaking, while the other two walls exhibited an extended loading plateau after the initial peak. All walls failed with cracking and block sliding along the main diagonals, a failure mode similar to conventional masonry. Proposals are made for modifying the equations for shear capacity from the Masonry Standards Joint Committee (MSJC) 2013 code for use in designing compressed earth block shear walls.

Composite beams are frequently used in building, combining a steel beam with either a concrete-filled steel deck or solid concrete slab. To ensure proper composite action, shear connectors, typically in the form of headed shear studs, are utilized. Traditionally, the strength assessment of these headed shear studs is made using empirical design specifications that are based on push-out tests, which have been widely conducted and standardized over the years. However, the standardized push-out tests have short-comings, such as uneven slab bearing, slab buckling, questions regarding the distribution of load to each stud, etc. A study was conducted to evaluate and compare the existing push-out test setup with two alternative test setups. The study also aimed to examine the behavior of headed shear studs in composite beams having deck deeper the current allowable limit of 3 in., as specified by American Institute of Steel Construction (AISC) design specification. While the standard specification allows for steel decks with rib heights of up to 3 in., there are deck profiles deeper than 3 in. available in the market. Utilizing these deeper decks in composite beams offers several advantages, including faster and more cost-effective construction by reducing the number of beams required. This research therefore found that a major challenge in creating an alternative test setup involves eliminating moment at the interface between the concrete-filled steel deck and the steel beam. This moment leads to tension in the headed shear stud/stud group closest to the actuator, thus affecting the shear strength of the headed shear studs. Further, these headed shear studs have significant strength when used with 3.5 in. decks but further research is necessary. / Master of Science / Composite beams are widely used in building construction, combining a steel beam with either a concrete-filled steel deck or a solid concrete slab. To ensure their proper function, shear connectors are used, typically in the form of headed shear studs. Traditionally, the strength of these shear studs is determined using standardized push-out tests, but these tests some challenges like uneven slab bearing, questions about even load distribution, etc. In this study, the existing push-out test setup was evaluated and compared with two alternative setups. The behavior of headed shear studs in composite beams with deeper decks than the current allowable limit specified by design standards was also investigated. Using these deeper decks offers advantages such as faster and more cost-effective construction. One major challenge in creating an alternative test setup was eliminating the moment at the interface between the concrete-filled steel deck and the steel beam. This moment caused tension in the headed shear stud closest to the actuator, impacting the overall shear strength of the studs. Additionally, it was found that these shear studs show promising strength when used with 3.5 in. decks, but more research is needed to fully understand their capabilities. By exploring new test setups and considering deeper decks, this research contributes to improving the design and construction of composite beams, making them more efficient and reliable for future building projects.

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.

Yes / This paper presents an experimental study on an innovative composite floor system that can be demounted and deconstructed. In this system, the composite slab, formed with profiled metal decking, was connected to a steel beam via demountable shear connectors. A full-scale demountable composite floor system specimen was tested to ultimate load bearing capacity and compared with a similar non-demountable composite floor system specimen using conventional welded headed stud connectors. The experimental results and observations showed that the structural behaviour and load bearing capacity of both composite floor systems are very similar. However, the composite floor system with demountable shear connectors could be deconstructed after testing and the composite slab could be easily detached from the steel beam. The comparison and analysis presented in this paper indicated that the simple design methods currently provided in the Eurocode 4 for the welded shear connections could be used to assess the ultimate moment capacity of demountable composite floor systems.

No / The formation of tribo-layers during machining is very common phenomena, especially when machining `free machining¿ steels. Several kinds of tribo-layers formed in metal cutting processes have been reported, layers of inclusions from the workpiece, oxide layers due to chemical reaction, plastic deformation layers, material transfer layers (MTLs) or built-up layers (BULs). A new tool¿chip contact model is proposed to explain the tribo-layer phenomena, which considers the nature of the shear strain rate distribution in the secondary deformation zone. A shear strain rate distribution in this zone having a shape similar to that found in the preliminary zone is proposed. A cutting interface (CI) is defined and this interface is at different location to the material boundary of tool and chip (MBTC). This difference is a key factor in the formation of the tribo-layer in the secondary deformation zone. This model can be used in improving tool wear prediction and the estimation of tool life.

yes / This paper presents an experimental study on shear strength, stiffness and ductility of demountable shear connectors in metal decking composite slabs through push-off tests. Twelve full-scale push-off tests were carried out using different concrete strength, number of connectors and different connector diameter. The experimental results showed that the demountable shear connectors in metal decking composite slabs have similar shear capacity and behaviour as welded shear studs and fulfilled the minimum ductility requirement of 6mm required by Eurocode 4. The shear capacity was compared against the prediction methods used for the welded shear connections given in Eurocode 4, AISC 360-10, ACI 318-08 and method used for bolted connection in Eurocode 3. It was found that the AISC 360-10 method overestimated the shear capacity while the ACI 318-08 method underestimated the shear capacity of specimens with single shear connector per trough. The Eurocodes method was found to provide a safe prediction for specimens with single and pair demountable connectors per trough. In addition, prediction methods given in both AISC 360-10 and ACI 318-08 for welded shear studs overestimated the shear capacity of specimens with 22 mm diameter demountable connectors that failed in concrete crushing. / PhD work from EPSRC studentship

Well-detailed reinforced concrete (RC) shear walls did not achieve the expected seismic performance in the 2011 Christchurch earthquake as per the Canterbury earthquake royal commission report. Similarly, RC shear walls showed low seismic performance in the 2010 Maule earthquake. The two major seismic events intrigued this research dissertation, where six half-scaled RC shear walls were constructed and tested. The six walls were split into two phases, each phase had different end configurations (i.e., rectangular, flanged, and boundary elements). Phase II RC walls had 2.4 times the vertical reinforcement ratio of Phase I walls. The walls were detailed as per CSA A23.3-19, and they were tested laterally under a quasi-static cyclic fully-reversed loading while maintaining a constant axial load through the full test of the walls. The overall seismic performance of the six walls is evaluated in Chapters 2 and 3 in terms of their load-displacement relationships, crack patterns, displacement ductility capacities, stiffness degradation trends, curvature profiles, end strains, energy dissipation capabilities, and equivalent viscous damping ratios. In addition, damage states are specified according to the Federal Emergency Management Assessment (FEMA P58) guidelines. The results came in agreement with the Canterbury earthquake royal commission report, where the test walls with low vertical reinforcement ratios showed lower-than-expected seismic performance due to the concentration of their plastic hinges at the primary crack locations. Moreover, the results validated the Christchurch (2011) and Maule (2010) earthquake findings as concentrating the rebars at the end zones and providing adequate confinement enhanced the seismic performance of the test walls, which was the case for Phase II flanged and boundary element walls. The displacement ductility variations of the test walls inspired the work of Chapter 4, where the objective is to develop a data-driven expression for RC shear walls to better quantify their displacement ductility capacities. In this respect, an analytical model is developed and experimentally validated using several RC walls. The analytical model is then used to generate a dataset of RC walls with a wide range of geometrical configurations and design parameters, including cross-sectional properties, aspect ratios, axial loads, vertical reinforcement ratio, and concrete compressive strengths. This dataset is utilized to develop two data-driven prediction expressions for the displacement ductility of RC walls with rectangular and flanged/boundary element end configurations. The developed data-driven expressions accurately predicted the displacement ductility of such walls and they should be adopted by relevant building codes and design standards, instead of assigning a single ductility-related modification factor for all ductile RC shear walls, as per the 2020 National Building Code of Canada. Several researchers tested well-detailed Reinforced Masonry (RM) shear walls and the results concluded that RM shear walls showed high seismic performance similar to that of RC shear walls. This intrigued the research efforts presented in Chapter 5, where a comparative analysis is performed between the six RC walls tested in this dissertation and three RM walls tested in a previous experimental program. The analysis focuses on comparing the seismic performance of both wall systems in terms of their crack patterns, load-displacement envelopes, curvature profiles, displacement ductility, normalized periods, and equivalent viscous damping ratios. In addition, an economic assessment is performed to compare such RC and RM shear walls using their total rebar weights and the total construction costs. Overall, RM shear walls achieved an acceptable seismic performance coupled with low rebar weights and low construction costs when compared to their RC counterparts. / Thesis / Doctor of Philosophy (PhD)

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