Yes / Recycled aggregate concrete filled stainless steel tube (RAC-FSST) is a new type of composite member combining the advantage of stainless steel and RAC. In this paper, a total of twenty-four RAC-FSST stub columns were tested under axial load, considering the influences of coarse recycled aggregate (CRA) content, steel ratios and compressive strengths of RAC. The obtained results, including the failure patterns, responses of axial load vs. deformation, stress states of external stainless steel tube and inner RAC and confinement effects, were systematically analyzed. Results indicated that all specimens presented good ductility and high residual strengths after reaching the maximum axial load. The elastic stiffness of RAC-FSSTs obviously declined with the increasing CRA content, while the strain at the ultimate load was larger. The inclusion of CRA could advance the occurrence of the confinement and lead to lower confining stress. Based on the experimental results, an analytical model with consideration of confinement action was developed to predict the axial response of RAC-FSST stub columns. Besides, the current design provisions for the normal CFST and RAC-FST members were employed to evaluate their applicability to RAC-FSSTs. In general, the design rules EN 1994-1-1:2004, GB 50936-2014 and T/CECS 625-2019 gave a conservative and relatively accurate prediction on ultimate strength of RAC-FSST stub columns. / This work was supported by the National Natural Science Foundation.

Abstract A new generation of EN 1992-1-1 (2004) also known as Eurocode 2 is under development and currently there is a set of proposed provisions regarding section 6.4 about punching shear, PT1prEN 1992-1-1(2017). It was of interest to compare the proposal with the current punching shear design provisions. The aim of this master thesis was to compare the punching shear resistance obtained in accordance with both design codes. Furthermore the eect of some parameters on the resistance was to be compared. It was also of interest to evaluate the userfriendliness of the proposal. In order to meet the aim, a case study of a real 　at slab with drop panels was performed together with a parametric study of a pure ctive 　at slab. The parametric study was performed for inner, edge and corner columns in the cases prestressed, without and with shear reinforcement. It was concluded that the distance av from the column axis to the contra 　exural location has a big in　uence on the punching shear resistance. The factor ddg considering concrete type and aggregate properties also has a big impact on the resistance. The simplied estimation of av according to 6.4.3(2) in PT1prEN 1992-1-1 (2017) may be inaccurate in some cases. The length b0 of the control perimeter has a larger eect on the resistance in EN 1992-1-1 (2004) than in PT1prEN 1992-1-1 (2017). In PT1prEN 1992-1-1 (2017), studs located outside the second row has no impact on the resistance. The tensioning force in a prestressed 　at slab has a larger in　uence on the resistance in PT1prEN 1992-1-1 (2017) than in EN 1992-1-1 (2004). Furthermore, the reinforcement ratio is increased by the tendons, and thus aect the resistance in PT1prEN 1992-1-1 (2017). Clearer provisions for the denition of the support strip bs for corners and ends of walls are needed in PT1prEN 1992-1-1 (2017). It may be questionable if the reduction of the perimeter for a large supported area in accordance with 6.4.2(4) in PT1prEN 1992-1-1 (2017) underestimates the resistance v in some cases. Considering the work-load with PT1prEN 1992-1-1 (2017), more parameters are included. However, they may not require that much eort to obtain. Keywords: Punching shear, resistance, concrete, 　at slab, design provisions, Eurocode 2, case study, parametric study, shear reinforcement, prestressed vi

A new version of EN 1992-1-1, Eurocode 2 for Design of Concrete Structures, is under development and one of the most discussed topics is shear capacity for prestressed concrete beams without shear reinforcement, partly because shear failure occurs suddenly and can have catastrophic consequences. For the new version of Eurocode, there are a total of three proposed equations to replace the two equations that currently exist in EN 1992-1-1 for shear capacity of prestressed concrete beams without shear reinforcement. One of the proposed equations is intended to replace the equation intended for beam regions where bending cracks do not occur. The other two equations are proposed for beam regions where bending cracks occur. One of the proposed equations for beam regions with bending cracks, is based on critical shear crack theory and takes the normal force in consideration, while the other equation for beam regions with bending cracks is like the one found today in Eurocode, an empirical equation, where the contribution of normal force is empirical. In this thesis, all equations have been set against each other and compared with the help of nonlinear finite element analyzes and experiments which Dr. De Wilder has done in his doctoral thesis. The impact of the prestressing force on the shear force capacity of beams has also been investigated. The results show that the equations for beam regions that do not have bending cracks give identical shear force capacities. While the equation which is based on critical shear crack theory takes the shear span into consideration and captures the effect of the shear span correctly, which the other proposed equation and the one found in Eurocode today do not and are on the unsafe side for increasing shear spans. Furthermore, it turned out that the equation which is based on critical shear crack theory was rather conservative, while the equation that exists today in Eurocode gives approximately the same shear capacity as the other proposed equation. Furthermore, it was found that if the amount of longitudinal reinforcement is reduced, at the same time as the prestressing force is unchanged, an insignificant reduction in the shear capacity on prestressed concrete beams is obtained. / En ny version av EN 1992-1-1, Eurokod 2 Dimensionering av betongkonstruktioner, är under utveckling och ett av de mest diskuterade ämnena är tvärkraftskapacitet för förspända betongbalkar utan skjuvarmering, bland annat eftersom huvudspänningsskjuvbrott uppstår plötsligt och kan få katastrofala konsekvenser. Till den nya versionen av Eurokoden finns det totalt tre föreslagna ekvationer för att ersätta de två ekvationer som för närvarande finns i EN 1992-1-1 för tvärkraftskapacitet för förspända betongbalkar utan skjuvarmering. En av de föreslagna ekvationerna är tänkt att ersätta ekvationen avsedd för balkregioner där böjsprickor ej uppstår. De andra två ekvationerna är föreslagna för balkregioner där böjsprickor uppstår. En av de föreslagna ekvationerna för balkregioner med böjsprickor är baserad på kritisk skjuvsprickteorin och tar hänsyn till normalkraftens bidrag till tvärkraftskapaciteten, medan den andra föreslagna ekvationen för balkregioner med böjsprickor är likt den som idag finns i Eurokoden, en empirisk ekvation, där normala kraftens bidrag är baserad på ett empiriskt tillägg. I detta examensarbete har alla ekvationer ställts mot varandra och jämförts med hjälp utav icke-linjär finit-elementanalyser samt experiment som Dr. De Wilder gjort i sin doktorsavhandling. Vidare har också förspänningskraftens påverkan på balkars tvärkraftskapacitet undersökts. Resultaten visar att ekvationerna för balkregioner som ej har böjsprickor ger identiska tvärkraftskapaciteter. Medan ekvationen som är baserad på kritisk skjuvsprickteorin tar hänsyn till skjuvspännvidd och fångar effekten av skjuvspännvidden korrekt, vilket den andra föreslagna ekvationen och den som finns i Eurokoden idag inte gör och är på den osäkra sidan för ökad skjuvspännvidd. Dessutom visade det sig att ekvationen som är baserad på kritisk skjuvsprickteori är tämligen konservativ, medan ekvationen som finns idag i Eurokoden ger ungefär samma tvärkraftskapacitet som den andra föreslagna ekvationen. Vidare visade det sig att ifall man minskar mängden längsgående armering, samtidigt som förspänningskraften är oförändrad, så fås en obetydlig minskning utav tvärkraftskapaciteten på förspända betongbalkar.