Search Results (9)

In the Middle East, wall-like reinforced concrete (RC) columns are a common choice in multistory buildings. Sometimes, these columns need axial retrofitting for increased load capacity. In practice, unstrengthened columns bear their load, and if retrofitting is necessary, the load is released before the upgrade—unlike in past research studies that overlooked this real-world scenario. This study aimed to investigate the response of preloaded wall-like RC columns after being retrofitted using different configurations. In the experimental campaign, two half-scale columns were cast and axially loaded to 80% of their capacity, and the load was then totally released. After that, these specimens were strengthened with two different schemes, and hence, they were concentrically loaded until failure. In both schemes, the section shape was not modified. The first scheme comprised wrapping carbon FRP (fiber-reinforced polymer) sheets together with near-surface mounted (NSM) steel rebars. However, the second technique was composed of wrapping glass FRP (GFRP) sheets together with NSM steel rebars and bolted steel plates. The second scheme was found to be superior to the first one due to the extra confinement provided by the bolted steel plates. This scheme improved the peak load, stiffness, and dissipated energy by 115%, 75%, and 524%, respectively. Other than the testing campaign, nonlinear numerical modeling was undertaken to examine the behavior of tested specimens. The models were utilized to conduct a parametric study, exploring the influence of the percentage of preloading and the amount of load release on the response of columns strengthened with the second scheme. Full article

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings. Full article

Reinforced concrete (RC) wall-like columns are commonly employed in structures in Saudi Arabia. These columns are preferred by architects owing to their minimum projection in the usable space. However, they often need strengthening due to several reasons, such as the addition of more stories and increasing the live load as a result of changing the usage of the building. This research aimed to obtain the best scheme for the axial strengthening of RC wall-like columns. The challenge in this research is to develop strengthening schemes for RC wall-like columns, which are favored by architects. Accordingly, these schemes were designed so that the dimensions of the column cross-section are not increased. In this regard, six wall-like columns were experimentally examined in the event of axial compression with zero eccentricity. Two specimens were not retrofitted to be used as control columns, whereas four specimens were retrofitted with four schemes. The first scheme incorporated traditional glass fiber-reinforced polymer (GFRP) wrapping, while the second one utilized GFRP wrapping combined with steel plates. The last two schemes involved the addition of near-surface mounted (NSM) steel bars combined with GFRP wrapping and steel plates. The strengthened specimens were compared with regard to axial stiffness, maximum load, and dissipated energy. Besides column testing, two analytical approaches were suggested for computing the axial capacity of tested columns. Moreover, finite element (FE) analysis was performed for evaluating the axial load versus displacement response of tested columns. As an outcome of the study, the best strengthening scheme was proposed to be used by practicing engineers for axial upgrading of wall-like columns. Full article

In most machine learning (ML) applications, data that arrive from heterogeneous views (i.e., multiple heterogeneous sources of data) are more likely to provide complementary information than does a single view. Hence, these are known as multi-view data. In real-world applications, such as web clustering, data arrive from diverse groups (i.e., sets of features) and therefore have heterogeneous properties. Each feature group is referred to as a particular view. Although multi-view learning provides complementary information for machine learning algorithms, it results in high dimensionality. However, to reduce the dimensionality, feature selection is an efficient method that can be used to select only the representative features of the views so to reduce the dimensionality. In this paper, an unsupervised feature selection for online dynamic multi-views (UFODMV) is developed, which is a novel and efficient mechanism for the dynamic selection of features from multi-views in an unsupervised stream. UFODMV consists of a clustering-based feature selection mechanism enabling the dynamic selection of representative features and a merging process whereby both features and views are received incrementally in a streamed fashion over time. The experimental evaluation demonstrates that the UFODMV model has the best classification accuracy with values of 20% and 50% compared with well-known single-view and multi-view unsupervised feature selection methods, namely OMVFS, USSSF, and SPEC. Full article

In RC (reinforced concrete) frame structures, wall-like columns are laid within the space occupied by masonry walls to maximize usable space and thus minimize the column projections into the usable area. These columns often require strengthening owing to various reasons, including increasing the number of stories, changes in building usage, and others. The use of a hybrid system comprising NSM (near-surface mounted) steel rebars combined with CFRP (carbon-fiber reinforced polymer) laminates may be considered a sound technique for strengthening such wall-like building columns. The prime aim of this study is to devise an efficient scheme using a hybrid NSM/CFRP system to strengthen existing RC wall-like columns. Six half-scale RC wall-like columns were prepared and tested under monotonic concentric axial compression. Two columns were unstrengthened to serve as control specimens (CW1 and CW2), and four specimens were strengthened using four different schemes (SW1, SW2, SW3, and SW4). As favored by architects, all strengthening schemes were designed so that the dimensions of the column cross-section were not increased. The effects of strengthening schemes on the enhancement of axial capacity, energy dissipated, and stiffness were evaluated to find the most efficient scheme. Among the four studied schemes, using vertical continuous NSM rebars in combination with the wrapping of the three CFRP layers onto the exterior column surface (in specimen SW2) was the most efficient as it enhanced the ultimate load capacity by 80%. Three-dimensional FE (finite element) analysis was also conducted to predict the response of test specimens. The test results matched well with the FE outputs, which justified the accuracy of the used constitutive models for concrete, steel rebars, and CFRP sheets. Full article

Experimental and numerical investigations on the retrofitting of half-scale wall-like reinforced concrete (RC) columns were conducted. The axial compressive behavior of the control un-strengthened wall-like RC column (having a section aspect ratio of four) was compared with the strengthened columns. The columns were strengthened by employing external confinement through fiber-reinforced polymer (FRP) wraps and/or steel/FRP strips with/without modification of the column cross-section. The characteristics of axial load versus displacement and strain curves were discussed. The experimental results were also compared with the numerical models, which were first validated against the previous studies. A reasonably close agreement was achieved between the numerical and the test results with an error in prediction of less than 10% for the peak load. With the different schemes used for confinement, the enhancement in the load capacity of strengthened columns was in the range of 30–42% of the control column. In addition, significant ductility improvements were seen in schemes that employed the FRP wraps after shape modification. Full article

A simulation-based probabilistic method is proposed for assessing the reliability of steel-lined and prestressed fiber-reinforced concrete (PFRC) slabs against the impact loads. The impact testing of several prestressed and non-prestressed FRC slabs of 800 × 800 × 100 mm in size was carried out. The experimental program involved projectile impact testing of prestressed and non-prestressed FRC slabs using a gas gun. Three parameters were varied for testing of slabs under the projectile impact, viz., a quantity of steel fibers in the concrete, steel lining on the backside of the slab, and the prestressing level. The probability-based reliability analysis of all the tested specimens was then performed to highlight the influence of steel lining, steel fibers, and prestress in enhancing the safety of RC (reinforced concrete) slabs against projectile impacts. Projectile impact velocity exceeding the slab’s ballistic limit was assumed to lead to the failure of the PFRC slab, i.e., the perforation failure of the slab. Study results indicate that when no steel fiber was present, slab reliability was low. Adding fibers to slabs increases slabs’ reliability significantly. Specimens with the highest steel fiber content (1.2%) showed the greatest increase in reliability. The steel lining on the back face makes the slab’s reliability almost doubled in comparison with those without lining. Additionally, steel lining makes the PFRC slabs as reliable as desired. It was further noticed that the prestressing helps in enhancing the slab safety against projectile impacts. Even a minimal amount of prestressing makes a noticeable improvement in the reliability of PFRC slabs. Full article

Concrete is classified as a multi-composite material comprising three phases: coarse aggregate, mortar, and interfacial transition zone (ITZ). Fine and coarse aggregates occupy approximately 70–85% by volume, of which coarse aggregate typically constitutes more than two-thirds of the total quantity of aggregate by volume. The current study investigates the concrete performance produced using various recycled construction and by-product industrial waste coarse aggregates. Six types of coarse aggregates: manufactured limestone, quartzite, natural scoria, by-product industrial waste aggregate, and two sources of recycled concrete aggregates with densities ranging from 860 to 2300 kg/m³ and with different strength properties were studied. To determine the coarse aggregate contribution to the overall concrete performance, lean and rich concrete mixtures (Mix 1 and Mix 2) were used. Mix 1 (lean mixture) consisted of a ratio of water to cement (w/c) of 0.5 and cement content of 300 kg/m³, whereas a higher quantity of cement of 500 kg/m³ and a lower w/c ratio of 0.3 were used for Mix 2 (rich mixture). The results showed that while the compressive strength for different aggregate types in Mix 1 was comparable, the contribution of aggregate to concrete performance was very significant for Mix 2. Heavyweight aggregate produced the highest strength, while the lightweight and recycled aggregates resulted in lower mechanical properties compared to normal weight aggregates. The modulus of elasticity was also substantially affected by the coarse aggregate characteristics and even for Mix 1. The ACI 363R-92 and CSA A23.3-04 appeared to have the best model for predicting the modulus of elasticity, followed by the ACI-318-19 (density-based formula) and AS-3600-09. The density of coarse aggregate, and hence concrete, greatly influenced the mechanical properties of concrete. The water absorption percentage for the concrete produced from various types of aggregates was found to be higher for the aggregates of higher absorption capacity. Full article

The formulas available in the literature for predicting the projectile impact response of reinforced concrete (RC) targets are generally developed based on the results of impact tests. Recently, however, in order to avoid performing involved and challenging projectile impact tests, the impact response of RC targets was predicted using the quasi-static punching response of RC slabs. In this paper, the concept is extended to concrete slabs strengthened with textile-reinforced mortar (TRM) or carbon fiber-reinforced polymer (CFRP) sheets externally bonded to the concrete surface. In 16 groups, 96 slabs of 600 × 600 × 90 mm size were cast and tested under quasi-static and impact loads. The slabs were reinforced with two types of reinforcement: ϕ8@100 mm and ϕ4@25 mm. The singly and doubly reinforced concrete slabs with rebar spacing of 100 mm were strengthened using externally bonded CFRP and TRM on the back side of the slab specimens. Two mixes of concrete, representing normal and high-strength concretes, were used. The results of the present study reveal that the CFRP and TRM strengthening of RC slabs enhanced the energy absorption in punching by 57–130% and 20–59%, respectively. The use of WWM in singly and doubly reinforced slabs also resulted in a 30–42% and 41–63% increase in energy absorption in punching, respectively. An earlier proposed model was modified to incorporate the influence of strengthening (CFRP and TRM) in the estimation of the projectile perforation energy of the strengthened RC slabs with the help of energy absorbed in their quasi-static punching. This perforation energy was then employed for predicting the ballistic limit of CFRP- and TRM-strengthened slabs. The predictions show good agreement with the experimentally observed ballistic limits. Full article