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International Concrete Abstracts Portal

Showing 1-10 of 808 Abstracts search results

Document: 

19-004

Date: 

January 1, 2020

Author(s):

Peter H. Bischoff

Publication:

Structural Journal

Volume:

117

Issue:

1

Abstract:

This paper evaluates the approach adopted by ACI 318-19 for computing deflection of reinforced concrete. Comparison is made with the European approach and Branson’s approach used in previous editions of ACI 318. The adopted approach uses a rational expression for the effective moment of inertia, Ie, with a reduced cracking moment that gives greater values of computed deflection for lightly reinforced slabs. The impact of this change on member stiffness and minimum thickness requirements related to immediate and long-term deflection limits for serviceability is evaluated for beams and one-way slabs. Appropriate limits for maximum service load and member span are provided for slabs, and more stringent requirements are needed for minimum thickness of beams. Information about two-way slabs is also provided.

DOI:

10.14359/51718072


Document: 

18-515

Date: 

January 1, 2020

Author(s):

Francesco Cavagnis, João T. Simões, Miguel Fernández Ruiz, and Aurelio Muttoni

Publication:

Structural Journal

Volume:

117

Issue:

1

Abstract:

The shear strength of beams and one-way slabs has been acknowledged for more than one century as one of the most complex, yet fundamental, topics to be addressed in structural concrete design. The experimental data used to investigate the phenomenon has traditionally been obtained from tests on simply supported beams subjected to point loading and recording only a limited amount of data (applied load and deflection in most cases). Following these experimental evidences, design formulas have been calibrated—in many cases in an empirical manner—by using large amounts of experiments in the form of databases. Also, mechanical models have been proposed as a rational approach to shear design, which can be conceptually very different and relies on different shear transfer actions. Discussions on the pertinence of these models are mostly based on the general agreement of the failure load to existing data sets more than on a critical review of their basic hypotheses. Within this context, the development of new measuring techniques, such as digital image correlation (DIC), enables a systematic and transparent examination of the shear crack development and of the role of the various potential shear-transfer actions. This allows for a scientific discussion on the correctness of the principles of the design approaches and allows understanding their pertinence and limitations. Based on these possibilities, the main hypotheses of the Critical Shear Crack Theory (CSCT) for shear design are examined in this paper. To that aim, the results of a specific test series on specimens tested under realistic loading conditions are reviewed. The results show that shear strength results from a combination of various shear-transfer actions depending on the development of shear cracks and their associated kinematics. On this basis, the applicability and pertinence of the CSCT main hypotheses are discussed and a complete mechanical approach is formulated. Also, it is shown that the CSCT can be formulated in a simple and consistent manner as closed-form design equations.

DOI:

10.14359/51718012


Document: 

18-419

Date: 

November 1, 2019

Author(s):

Manik Barman, Julie M. Vandenbossche, and Donald J. Janssen

Publication:

Structural Journal

Volume:

116

Issue:

6

Abstract:

The joint performance of concrete slabs has a significant role in the development of faulting and fatigue cracks in full-depth concrete pavements and overlays. The joint performance refers to the load-related responses of a concrete pavement slab relative to its adjacent slabs. The higher the joint performance, the longer the life of the concrete pavement. The joint performance between the concrete slabs of undoweled joints or across cracks is achieved through aggregate interlock, which largely depends on the concrete strength, crack width, and crack surface texture. The use of structural fibers also influences the crack width, aggregate interlock, and, overall, the joint performance. The objective of this study is to develop an affordable small-scale joint performance test method so that the contribution of the concrete constituents and fibers, if used toward, can be quantified during the concrete mixture design stage. This will enable a better prediction of the life the concrete pavement. The proposed method uses 152 x 152 x 610 mm (6 x 6 x 24 in.) beams to characterize the joint performance of the concrete.

DOI:

10.14359/51718067


Document: 

18-241

Date: 

November 1, 2019

Author(s):

Mostfa Al Azzawi, Gray Mullins, and Rajan Sen

Publication:

Structural Journal

Volume:

116

Issue:

6

Abstract:

This paper investigates the influence of concrete porosity on durability of the bond between fiber-reinforced polymer (FRP) and concrete. Twenty-four slab specimens were cast using three different concrete mixtures with water-cementitious materials ratios (w/cm) of 0.53, 0.41, and 0.21, representing high, medium, and low porosities, respectiviely. The slabs were preconditioned by oven-drying and two commercially used carbon fiber-reinforced polymer (CFRP) materials bonded to surfaces that had been sand-blasted to provide a concrete surface profile (CSP) 3 rating. Repaired specimens were submerged in 30°C (86°F) potable water for 15 weeks and residual bond was evaluated through pulloff tests. Results showed 1 to 3% bond reduction in the high-porosity, low-strength concrete compared to a reduction in excess of 20% in its low-porosity, higher-strength counterpart. The likely reason for the better performance was deeper epoxy penetration into the more porous concrete substrate. Findings suggest that surface preparation and installation methods that allow epoxy to penetrate deeper into low-porosity, high-strength concrete can result in increased durability under moisture exposure.

DOI:

10.14359/51716801


Document: 

18-227

Date: 

November 1, 2019

Author(s):

Masoud Ghahremannejad, Ali Abolmaali, and Maziar Mahdavi

Publication:

Structural Journal

Volume:

116

Issue:

6

Abstract:

An increase in the fill height of buried box culverts leads to an increase in the thickness of the slab and wall, as well as in the number or size of longitudinal slab reinforcements required to resist flexure. This geometrical configuration imposes a shear behavioral mode. This study focuses on determining the shear strength of reinforced concrete (RC) box culverts with uniformly distributed load at the top slab. A framework, consisting of several subframes, was designed to convert the single displacement applied at the top of the framework to the equivalent uniformly distributed forces at the top slab of the culvert, allowing a displacement control analysis algorithm to be performed. To validate the loading mechanism, using the proposed framework, the load was applied on the top of an RC beam in the laboratory, and numerical studies were conducted. After validation, two sizes of RC box culverts were experimentally and numerically investigated. The results from the experimental program and verified numerical models differed from ACI 318-14 formulation for the shear strength of top slabs of RC box culverts.

DOI:

10.14359/51716800


Document: 

18-421

Date: 

September 1, 2019

Author(s):

Raffaele Cantone, Miguel Fernández Ruiz, Jan Bujnak, and Aurelio Muttoni

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

Punching reinforcement systems have significantly developed in recent years as they allow enhancing the punching resistance of slab-column connections as well as their deformation capacity. These systems, with varying geometry and layout, normally consist of vertical or inclined shear reinforcement with both ends anchored on the compression and tension side of the slab. For very high levels of load, when even common punching reinforcement systems cannot safely ensure the transfer of loads, steel shear heads are usually embedded in the slab to enhance the resistance of the connection. Yet, shear heads might be expensive and difficult to place in construction sites. Following the principle of the dowel action of the compression reinforcement, this paper introduces a novel system to efficiently reinforce slabs against punching shear by using large-diameter double-headed studs acting as shear dowels. This system enhances the performance of shear-reinforced slabs with respect to conventional solutions and might be an efficient alternative to shear heads for a large number of practical situations. The system is validated by means of a specific experimental program including 11 axisymmetric punching tests on interior slab-column connections. The results demonstrate not only the increase of the punching strength but also the deformation capacity of the connection. It is also shown that the system can be consistently designed accounting for the doweling forces by making use of the theoretical frame of the Critical Shear Crack Theory (CSCT), allowing to understand the activation of the shear dowels on the basis of the deformation of the member.

DOI:

10.14359/51716842


Document: 

18-406

Date: 

September 1, 2019

Author(s):

Aishwarya Y. Puranam and Santiago Pujol

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

Building codes control the minimum and maximum amounts of longitudinal reinforcement in reinforced concrete (RC) elements to avoid brittle failure. A two-phase experimental investigation was conducted to reexamine the existing limits to allow the use of high strength steel reinforcement (HSSR) with fy > 80 ksi (550 MPa). The test results suggested that it is feasible to use HSSR (with fy up to 120 ksi [830 MPa]). Careful projection of existing limits to HSSR produced elements with similar toughness as those with conventional reinforcement (Grade 60, fy = 60 ksi [415 MPa]). The results presented also supported code provisions to allow the use of HSSR introduced in ACI 318-19.

DOI:

10.14359/51716762


Document: 

18-400

Date: 

September 1, 2019

Author(s):

Bijily Balakrishnan and Devdas Menon

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

The application of yield line analysis to carry out strength design of reinforced concrete (RC) slab systems is mostly limited to solid slabs without beams. In an earlier paper on isolated rectangular beam-slab systems, the authors had demonstrated that such analysis, considering plastic hinges in the beams along with yield lines in the slabs, can result in rational and economical designs. In this paper, it is shown that such yield line analysis can be further extended to beam-slab systems with secondary beams, and the predictions have been validated by tests carried out on four rectangular RC beam-slab systems (each comprising four symmetric grid units), supported at the four corners on pillars. Six possible collapse mechanisms have been investigated. It is established that the critical collapse mechanism is governed primarily by the beam-slab relative strength. It is shown how an economical and rational design can be achieved, making use of the proposed yield line analysis.

DOI:

10.14359/51716760


Document: 

18-346

Date: 

September 1, 2019

Author(s):

Ahmed E. Salama, Mohamed Hassan, and Brahim Benmokrane

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

Recent years have seen a great interest in testing concrete slab-column connections reinforced with glass fiber-reinforced polymer bars (GFRP-RC). Yet, current fiber-reinforced polymer (FRP) codes and guidelines have not addressed the design of slab-column connections with FRP shear reinforcement. Results from an experimental investigation aimed at evaluating the effectiveness of glass fiber-reinforced polymer (GFRP) stirrups as shear reinforcement in edge slab-column connections reinforced with GFRP bars are presented. Four full-sized slabs with and without stirrups as shear reinforcement were tested to failure under combined vertical load and unbalanced moment. The effect of the GFRP stirrup type and extension on the punching shear response of the tested slab-column connections are analyzed and discussed. In addition, simplified design provisions to predicate the ultimate shear capacity of the tested specimens are proposed. The test results revealed that the presence of GFRP shear reinforcement as either closed or spiral stirrups within the slab around the column perimeter improved the punching-shear response of the tested connections. The results also indicated that the performance of the spiral stirrups was equivalent to or better than that of the closed stirrups in reducing the brittleness of the tested specimens with the same amounts of flexural and shear reinforcement. The proposed design provisions as extensions to those in CSA S806 design code yielded good, yet conservative predictions with an average Vtest/Vpred of 1.28 ± 0.24 for test specimens with FRP shear stirrups, as well as others with different types of FRP shear reinforcement found in the literature. This represents a step forward for engineers in designing two-way concrete slabs reinforced with FRP stirrups.

DOI:

10.14359/51716757


Document: 

18-036

Date: 

September 1, 2019

Author(s):

Yail J. Kim and Junhao Gao

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

This paper presents a new concept of high-performance structures composed of internally cured concrete and glass fiber-reinforced polymer (GFRP) reinforcement. The former addresses autogenous shrinkage that leads to premature cracking of concrete, and the latter provides a noncorrosive service environment. Presaturated superabsorbent polymer (SAP) is mixed with concrete at 0 to 0.4% of the cement mass to facilitate a hydration process. The swelling kinetics of SAP due to water absorption is quantified, and its releasing rate with time is determined. A total of 15 one-way slabs are tested in flexure to examine the effects of SAP inclusions. The behavior of the slabs is assessed by deterministic and stochastic models with an emphasis on tension stiffening and performance reliability. The amount of the internal curing agent affects the strength of the concrete and the response of the slabs. Various cracks are observed when the slabs are loaded, including flexural, horizontal splitting, and diagonal tension cracks. As the amount of SAP increases, the cracks become localized and expedite the failure of the slabs. The tension stiffening of control slabs (0%SAP) is more pronounced than that of the slabs with SAP. The cumulative degradation probability and the risk level of the slabs made of the internally cured concrete are controlled by the amount of SAP.

DOI:

10.14359/51715574


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