Flexural Performance of Concrete T-Beams Reinforced with UHPC: Experimental and Theoretical Analysis

Concrete T-beams are commonly used in building slab systems and bridge decks. They may require strengthening in shear when they are deteriorated or when loading requirements increased. This research project studied the shear behaviour of concrete T-beams using cast-in-place Ultra High-Performance Concrete (UHPC) layers as a lateral strengthening method avoiding beam depth modification. Three UHPC strengthened beams together with one reference reinforced concrete beam were tested in monotonic three-point bending. Parameters investigated include the thickness of UHPC layers and the presence of steel anchors at the UHPC-concrete interface. A digital image correlation (DIC) technique was used to investigate the strain distribution of T-beams during the testing. Strain distribution, failure modes and strengthening effects provided by the UHPC lateral strengthening were analyzed. Results show that UHPC strengthening can substantially improve the stiffness and shear capacity of concrete T-beams, 25 and 50 mm lateral layers increased by 102% and 113% the T-beam shear capacity, respectively. Typical bending-shear behaviour were observed on each strengthened beam with UHPC layers. A final shear failure was observed in the T-beam with 25 mm UHPC layers and 50 mm UHPC layers without anchors, while a combination of shear and bending failure was noted in the T-beam with 50 mm UHPC layers and steel anchors. The steel anchors at the UHPC-concrete interface can further increase the ultimate shear capacity and beam stiffness, but at a limited extent. Therefore, experimental results confirmed that cast-in-place UHPC lateral layers are an effective way to strengthen existing concrete T-beams with inadequate shear capacity

Eccentrically compressed behavior of UHPC columns considering the P-delta effect

Torsional behavior of ultra-high performance concrete (UHPC) rectangular beams without steel reinforcement: Experimental investigation and theoretical analysis

To improve the flexural performance of damaged reinforced concrete T-beams, a method of filling ultra-high performance concrete (UHPC) in the damaged area was adopted. Experimental studies were conducted on two UHPC-reinforced concrete T-beams with different lengths of damaged areas and one undamaged concrete T-beam as a reference. Crack distribution, failure modes, cracking loads, flexural capacities, and strain variation of the specimens were analyzed. Subsequently, a nonlinear finite element (FE) model of the UHPC-reinforced T-beam was developed using ABAQUS, and the FE model results were compared with the experimental results to validate the accuracy of the FE simulation method. The results indicated that the two UHPC-reinforced T-beams exhibited a similar flexural failure process to the undamaged T-beam. The longitudinal tensile strain distribution at the mid-span section showed that the composite section formed by the filling of UHPC in the damaged region still adhered the assumption of the planar section. Owing to the excellent bond performance between UHPC and the existing concrete, the main cracks of the UHPC-reinforced T-beams appeared in the chiseled area, and the crack widths of the UHPC-reinforced T-beams under the same load were smaller than those of the reference T-beam. Overall, the reinforcing method of filling UHPC in the damaged region can restore or even enhance the flexural performance of the damaged reinforced concrete T-beams.

Structurally deficient bridges are commonly retrofitted using conventional methodologies, including reinforced concrete, steel jackets, and fiber-reinforced polymers. Although these retrofit methods aim to improve structural performance, exposure to aggressive environments may undermine the durability performance of the retrofit material. More recently, ultra-high-performance concrete (UHPC) has provided an alternative to conventional construction methods, with its superior material characteristics favoring its use in retrofit applications. In this study, a large-scale reinforced concrete (RC) T-beam is constructed and artificially damaged. The T-beam is then retrofitted with an external envelope of UHPC on all faces. Sandblasting is introduced to the surface, providing partially exposed reinforcement in the T-beam to simulate material deterioration. Additional reinforcement is placed in the web and flange, followed by casting the enveloping layer of UHPC around the specimen. The feasibility of this method is discussed, and the structural performance of the beam is assessed by subjecting the beam to cyclic and ultimate flexural loading. This paper presents the results of cyclic and ultimate testing on the RC-UHPC composite T-beam regarding load-displacement, failure mode, and strain responses. The retrofitted T-beam specimen is subjected to a cyclic loading range of 131 kN for 1.576 million cycles. Despite no visible cracks in the cyclic testing, the specimen experiences a 12.22% degradation in stiffness. During the ultimate flexural testing, the specimen shows no relative slip between the two concretes, and the typical flexural failure mode is observed. By increasing the longitudinal reinforcement ratio in the web, the failure mode can shift from localized cracking, predominantly observed in the UHPC shell, toward a more distributed cracking pattern along the length of the beam, which is similar to conventional reinforced concrete beams.

Flexural behavior of UHPC joints for precast UHPC deck slabs

To address the bottleneck issues of traditional concrete T-beams, such as excessive self-weight, susceptibility to cracking, and insufficient durability, this study investigates the flexural performance of Ultra-High-Performance Concrete (UHPC) T-beams. Through systematic experiments, the combined effects of three UHPC material ratios and three rebar schemes were analyzed. Six UHPC T-beam specimens were designed, and flexural performance tests were conducted using a staged loading approach, focusing on crack propagation, failure modes, and load-deflection curves to reveal their mechanical behavior and failure mechanisms. The results indicate that steel fibers significantly enhance UHPC toughness. At a fiber content of 1.5%, the specimens exhibited a yield load of 395–418 kN, with an ultimate load increase of 93% compared to the fiber-free specimens. The failure mode transitioned from brittle shear to ductile flexural. Increasing the rebar ratio improved load-bearing capacity, with a 4.58% rebar ratio yielding an ultimate load of 543 kN (51% higher than B1-02), but reduced ductility by 36%. Steel fibers restricted crack widths to 0.1 mm via crack-bridging effects, raising the cracking load by 53% and the shear capacity by 2.8 times. UHPC mix ratio adjustments had a limited impact on beam performance at the same fiber content. Overall, UHPC T-beams exhibited a compressive concrete crushing-dominated failure mode, with load-deflection curves showing a 42% gentler slope than conventional concrete. The ductility coefficient ranged from 3.8 to 5.2. For engineering applications, it is recommended to maintain a steel fiber content of at least 1.5% and a rebar ratio of 2.5–4.0% to strike a balance between strength and ductility.

Bending behaviour of reinforced concrete T-beams damaged by overheight vehicle impact strengthened with ultra-high performance concrete (UHPC)

Experimental study, finite element simulation and theoretical analysis on failure mechanism of steel–concrete-steel (SCS) composite deep beams with UHPC

This study aims to achieve the swift and precise classification of ductile and brittle failure modes in flexural reinforced concrete (RC) members, specifically those with tension sides strengthened by ultrahigh performance concrete (UHPC). Employing six ensemble learning techniques—Bagging, Random Forest, AdaBoost, Gradient Boosting, XGBoost, and LightGBM—the authors utilize a comprehensive dataset comprising 14 features, which include manually labeled failure modes obtain from load–deflection curves. The model training spans four scenarios, varying in the inclusion or exclusion of features describing the cross-sectional area of RC members and moment resistance. XGBoost emerges as the most effective classifier, achieving an impressive 84% accuracy with high confidence. Additionally, the study employs the Shapley Additive Explanation (SHAP) technique on the best-performing model to illuminate the significance and impacts of various features in UHPC-strengthened flexural members’ failure modes. Notably, moment resistance and UHPC tensile strength surface as the most influential factors in predicting failure modes. Increased rebar yield strength, UHPC compressive strength, UHPC reinforcement ratio, and steel fiber volume in UHPC contribute to enhanced ductility in flexural members, while heightened moment resistance and UHPC layer thickness, along with a robust RC-UHPC interface, tend to induce brittleness. The introduction of such an effective failure modes classification model, coupled with the model’s explainability, instills trust in its predictions and facilitates seamless integration into real-world applications, particularly in seismic areas. The model’s ability to operate without the need for pre-experimental tests marks a significant advancement in the field.

Experiment on an externally prestressed ultra high performance concrete (UHPC) box girder sub- jected to symmetrical concentric loads is carried out. The behavior of the test girder is investigated, including the load-deflection curve at mid-span, cracking pattern, strain distribution, and failure mode. The mid-span nominal moment capacity of the girder is analyzed. Test results show that the anti-cracking capacity of UHPC box girder is better than that of a normal prestressed concrete (PC) girder. The tensile property of UHPC should be taken into account in the process of calculating mid-span nominal moment capacity of the externally prestressed UHPC box girder. Finite element (FE) model analysis results agree well with the test results. The influencing parameter, concrete grades, was studied numerically to compare the flexural behav- ior of UHPC girder with PC girder. The cracking moment and ultimate load calculation method is proposed, which can meet precision for engineering practice and can be a reference method for design calculation of a prestressed UHPC box girder.

Experimental study on the uniaxial compression performance of ultrahigh-performance concrete constrained by stirrups and fibers

Tensile performance of UHPC-filled grouted corrugated duct connection for large-diameter rebars in prefabricated canopies

Flexural behaviors of a novel precast hollow UHPC composite beam reinforced with inverted T-shaped steel: Experimental investigation and theoretical analysis

<p>This paper mainly studies the bonding mechanism of ribbed steel reinforcing bars in ultra-high performance concrete (UHPC) considering the influence of material ductility. In recent years, the bond slip behavior of reinforcing bars in UHPC has received extensive attention. In the previous pull-out tests, it was found that the classical splitting theory still plays role in bond failure modes. In this paper, the pull-out test is simulated by finite element analysis, and it is found that unlike ordinary concrete, UHPC can still hold the load for a period of time after the tensile stress on splitting surfaces reaches the critical value, due to the ductility of the material. It is found from the numerical results that the bonding stresses are not evenly distributed along the steel bar when the pull-out failure occurred. Through theoretical analysis and experimental verification, the maximum bonding force of ribbed reinforcing bars in UHPC is closely related to the material ductility. Based on this, a new theoretical model for calculating the bonding strength of ribbed steel reinforcing bars in UHPC is proposed, and can be used for the design method of urban bridge built with UHPC.</p>