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Highlights • The LTSFC possess high potential to enhance the impact strength. • The LTSFC possess high potential to minimize drawbacks of the conventional FRC. • Innovative LTSFC technology for protection of civilian and military structures under terrorist attack. Abstract This study pioneers the concept of a novel layered two stage fibrous concrete (LTSFC) subjected to falling weight collision. The LTSFC is a newly developed concrete, with unique combination of steel fibres and coarse aggregates that are premixed and preplaced in the formwork in three layers followed by a flowable grout injection in each layer to fill the voids. In this study, some LTSFC slabs were proposed to consider the combined effect of layered and two stage concrete containing different type and combinations of steel fibres. Nine slabs were proposed, casted and tested, for which firstly the LTSFC were prepared and reinforced in three layers of 4%, 2% and 4% with three different fibres viz., crimped fibre (CF), hooked end fibre (HF), combined CF and HF and combined long and short CF. Secondly, the slabs were reinforced with 3.3% of same type of steel fibres over the entire cross section. The average amount of fibre used in LTSFC specimen was 3.3% which is similar to the fibre dosage used in the second series, where the fibres are equally spread in entire cross section. The study parameters viz., number of repeated impacts that induce the first crack and failure, impact ductility ratio, crack resistance (service and ultimate) and impact crack resistance ratio were considered herein. The results indicated that LTSFC specimens exhibited significant increase in the number of repeated impacts for the initial crack and failure to occur, high crack resistance, enhanced ductility and impact crack resistance ratio when related with non-fibrous concrete. Hence, the most significant findings of this research should stimulate innovation and new technology to develop the novel LTSFC in future studies. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted on empty and grouted stainless steel square hollow section (SHS) tubular X- and T-joints subjected to axial compression. A total of 24 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors ( β , τ , grouting and grout strength) on the behaviour of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel SHS tubular X- and T-joints generally increased with the increase of the β and τ values. The enhancement of joint strengths obtained from grouting both brace and chord members is much greater than that obtained from grouting chord member only. In addition, the ultimate strengths of stainless steel SHS tubular X- and T-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel SHS tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally conservative for the design of empty stainless steel SHS tubular X- and T-joints subjected to axial compression, but unconservative for the design of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate. [ABSTRACT FROM AUTHOR]

Abstract: In a previous research study the authors performed push-out tests with smooth micropile inserts grouted under varying confinement conditions. It was shown that: (i) failure always occurs at the steel-to-grout interface; and (ii) the connection capacity increases with the passive confinement. To increase the connection capacity, it is a common practice to weld steel rings on the surface of the micropile and execute grooves in the predrilled hole. Therefore, a new study is herein presented aiming to widen the conclusions already drawn by analysing the influence of most important parameters in the bond strength of textured micropiles grouted to concrete footings. Laboratory tests were specifically designed for assessing the effect on the connection capacity of the: (i) diameter of the predrilled hole; (ii) insert’s embedment length; (iii) active confinement of the footing; and (iv) treatment of the hole surface. Eighteen textured micropile inserts grouted in RC footings were submitted to monotonic push-out tests until failure. In brief, it can be stated that the capacity of the micropile-to-footing connection increases by increasing the insert’s embedment length and by decreasing the hole diameter. Moreover, an adequate active confinement must be provided to achieve the required capacity. [Copyright &y& Elsevier]

Abstract: The hot spot stress concentration factors (SCFs) for an as-welded tubular joint can be reduced by infilling the chord member with cementious grout, with associated improved fatigue strength for the grouted joint. However, inconsistent fatigue test results of grouted tubular joints are found in the published literature, which cannot be justified by hot spot stress approach. In order to obtain a better understanding for the fatigue performance of grouted tubular joints, a comprehensive fracture mechanics study is carried out for the reported fatigue test on as-welded tubular T-joint and another joint with grouted chord. The stress intensity factors (SIFs) of the two joints are determined by numerical method and then by empirical method. The SIF results are found to be consistent and in agreement of the fatigue test results. The presence of infilled grout in the chord is found to reduce the SCF, and lower the degree of bending (DOB). For tubular joints with weld toe fatigue cracking, the hot spot stress with lower DOB is associated with larger crack driving force and is more damaging than that with higher DOB. Hence, for fatigue assessment of grouted tubular joints it is essential to include the effect of DOB, which is ignored in hot spot stress S–N approach recommended in some current design codes. [Copyright &y& Elsevier]