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Reinforced concrete flat solid slabs may experience explosive and impact loads. Reinforced concrete flat solid slabs have been studied under static and dynamic loads. Researchers have widely explored numerous reinforcing strategies to strengthen RC slabs exposed to impact loads, yet gaps remain. Internal anchorage stirrups (W-stirrups shear reinforcement) is still rarely used to strengthen slabs against impact loading. Consequently, this study emphasized the influence of W-stirrups shear reinforcement on the dynamic response and failure modes of RC slabs subjected to impact loads.The first part examined the impact behavior of fully fixed RC flat solid slabs reinforced with W-stirrups shear reinforcement experimentally. Slabs were impacted using portable drop-weight testing equipment. Six 800-x-800-x-90-mm RC slabs were made. Three samples were reinforced with a W-stirrups orthogonally oriented in two directions, whereas three controls were without any type of strengthening. The eccentric vertical displacement of slabs, strain at four points on the W-stirrups, two on main steel, and two on concrete, and acceleration at one point over a slab were measured; also, failure modes were monitored.In the second section, ABAQUS software was used to generate finite element models of slab study samples. Numerical model results matched experimental results. Thus, the suggested finite element model may assess reinforced RC slabs under low-velocity impact loads. Finally, a parametric study was conducted in the third part to address the issue of over-reinforced design in slabs with W-stirrups. The parametric study aimed to determine the optimal steel ratio of flexural and shear reinforcement and its influence on the behavior of RC flat solid slabs reinforced with W-stirrups shear reinforcement.

An internal strengthening system involving the embedding of a post-tensioned prestressing tendon in a wedge-shaped anchorage of an existing concrete member was developed previously. The previous study confirmed the adequate load capacity of the prestressing tendon for the internal strengthening technique. The tendons used in the previous investigation were steel-rigid bar and steel-wire cables. These steel tendons are prone to corrosion under severe environmental conditions, such as bridge deck slabs sprayed with deicers. Carbon fiber composite cables (CFCC) are occasionally employed as tendons in prestressed concrete bridges. This study focused on the non-metallic material and examined the load capacity of CFCC tendon in internal strengthening systems to achieve the feasibility of the technique under corrosive environment. The main concern of the novel strengthening system was the anchoring system of the CFCC in the internal wedge. In general, both ends of the CFCC tendon can be gripped with external fasteners and be provided a tensile force using a hydraulic jack. In an internal prestressing system, a CFCC end must be anchored without any external fastener. It is preferable to simply fix the CFCC in a small wedge anchor made of existing concrete. This study focused on developing a CFCC anchoring method in a wedge-shaped hole and examined the tensile load capacity of the CFCC tendon fixed in the anchorage. The end of the CFCC tendon was reversely twisted to improve the pullout resistance by increasing the diameter of the cable. To examine the load-bearing capacity of the developed CFCC tendon, a mock-up reinforced concrete (RC) block with an internal wedge-shaped anchorage was used. A CFCC tendon equipped with a reverse-twisted tip was inserted into a wedge-shaped hole filled with high-strength grout. A pull-out test of the CFCC tendon was conducted to examine its load-bearing capacity. The test results revealed that the CFCC tendon with a reverse-twisted tip embedded in the anchorage exhibited adequate load-bearing capacity. This study confirmed that the post-tensioned prestressing system using the CFCC tendon is appropriate for strengthening RC members having the thickness of at least 200 mm, such as bridge deck slabs.

A new strengthening system, which embeds a post-tensioned PC bar tendon into the wedge-shaped anchorage of an existing concrete member, was developed. Previously, the adequate load-bearing capacity of the prestressing tendon anchorage was confirmed on simple element specimens. In the present study, the developed system is applied to the addition of new concrete members to old concrete structures. The strengthening effect of the system was examined in a loading test on jointed full-scale concrete members. The saltwater permeability at the joint was also examined. The flexural properties of the jointed members were compared to those of concrete beams jointed with conventional post-installed adhesive anchors. The concrete beams jointed by the proposed system exhibited superior crack-resistance and load-carrying capacity, and their joints were strongly water-impermeable. [ABSTRACT FROM AUTHOR]

The present study aims to develop a strengthening system using prestressing tendons embedded into an internal anchorage of concrete member. The internal anchorage, a wedge-shaped hole, is made by using a special drilling machine. The tip of the hole is filled with high strength mortar to anchor firmly the prestressing tendon. The strengthening system is acceptable even in relatively narrow workspaces, and also applicable for joints between existing and additional concrete members. The experimental study conducted a pull-out test of the prestressing tendon to examine the load-bearing capacity. A finite element simulation was also performed to confirm the bonding and unbonding effects of the prestressing tendon. The test result confirms adequate load-bearing capacity of the anchorage for the prestressing tendon. In addition, the FE simulation shows that the strengthening system can provide a constant prestress even if the prestressing tendon is not bound to the mortar in the anchorage. [ABSTRACT FROM AUTHOR]

• Corrugated pipe with steel-wires can be used for an internal strengthening system. • The corrugated pipe doubled as a grouting pipe for the wedge-shaped anchorage. • Pull-out tests confirmed adequate load capacity of the anchorage-embedded tendon. • A material suitable for use as filling for horizontal grouting was found. The present study focused on creation of an internal strengthening system, which involved embedding a post-tensioned PC tendon in a wedge-shaped anchorage of an existing concrete member. Under conditions with narrow work spaces, it was difficult to employ the previous system using a post-tensioned prestressing bar, as adequate backspace was required to install the bar. A flexible hollow corrugated pipe covered with steel wire cables seemed applicable even in such narrow spaces. Interestingly, the hollow stranded tendon could also be used as a grouting-pipe to fill the internal anchorage. The foci of this study were to develop a grouting material suitable for passage through a hollow corrugated pipe, and to determine the applicability of the hollow-type prestressing tendon for the internal strengthening system. In the study, a horizontal grouting test was first conducted using 5 m-long corrugated pipes of 10 mm internal diameter. It was confirmed from the grout and strength tests that some grouting materials were applicable for filling the hollow-type PC strands. In addition, pull-out tests of the prestressing tendon embedded in the anchorage of mock-up RC blocks were conducted to examine their load-bearing capacity. Furthermore, visible tests of the horizontal and upward grouting were conducted to confirm the filling condition in the wedge-shaped anchorage. The test results confirmed adequate load-bearing capacity of the hollow prestressing tendon embedded in the anchorage when the filler applicable to horizontal grouting was used. [ABSTRACT FROM AUTHOR]