ACI Model Research Articles

Abstract 501: Selective i n vivo Modulation of Vagal-Muscarinic Signaling Prevents Sudden Cardiac Death in a Pressure Overload Model of Heart Failure

Introduction: Sudden cardiac death (SCD) from ventricular tachyarrhythmias (VT/VF) claims a quarter millions lives/year in USA. Patients with heart failure (HF) have high SCD risk. We previously demonstrated that differential remodeling of cardiac muscarinic receptors plays a critical role in pathogenesis and for effective therapy of HF and SCD risk [PMID: 25733594]. Ongoing clinical trials of chronic vagus nerve stimulation (cVNS) aimed at improving left ventricular (LV) function in HF patients have had mixed preliminary results. However, the effect of cVNS on SCD risk is unexplored. While acute VNS terminates VT/VF, cVNS likely alters the arrhythmogenic substrate. A better understanding of the underlying mechanisms is necessary for the design of new, more effective therapies. Hypothesis: cVNS prevents SCD by reducing calcium, autonomic and redox derangements in LV myocytes and improving repolarization reserve in pressure overloaded hearts. Methods: Guinea pigs are randomized to Sham or aortic constriction (AC) with daily brief (30-min) low-dose β-adrenergic stress (Shami; ACi), with and without in vivo cVNS therapy via an implanted device, with and without in vivo end-organ muscarinic receptor blockade (MRB) using glycopyrrolate. Echocardiography and continuous 24-hour ECG analyses are performed. Animals are sacrificed at 4 weeks for biochemical, excised perfused heart (pressure-volume, electrophysiology, optical mapping) and isolated LV myocyte studies at 37°C. PRELIMINARY RESULTS: Compared to Sham, the M2 subtype of muscarinic receptors are upregulated in AC and ACi, along with reduced calcium cycling, sarcomere shortening and β-adrenergic responsiveness. Whereas ACi+MRB markedly increased SCD incidence, ACi+cVNS prevented SCD. Interestingly, cVNS prolonged but also stabilized the ECG QT interval by reducing dispersion of repolarization in ACi model. Echocardiographic fractional shortening was also higher in ACi+cVNS (52±1%; 4 weeks) compared to ACi (27±2%; 4 weeks) and ACi+MRB (23±5%; 2 weeks). Conclusions: Chronic in vivo perturbation of cholinergic signaling may be an effective strategy for SCD therapy. Ongoing experiments are aimed at dissecting underlying mechanisms and identifying potential targets for SCD therapy.

A compression field based model to assess the shear strength of concrete slender beams without web reinforcement

Concrete elements such as slabs, footings and some types of beams are usually designed without web reinforcement, meaning that the shear force must be resisted by concrete only. However, current design provisions such as ACI, Eurocode 2 and CSA use sectional methods to assess the shear strength of such elements. Such methods are empirical or semi-empirical at best, and thus, in certain situations, they may lead to an inaccurate assessment of the shear strength. In this paper, a compression field based model to assess the shear strength of concrete slender beams was proposed. The proposed model is less dependent on the empirical approach than other existing models, which gives it an advantage when assessing unconventional cases. The accuracy of the proposed model as well as ACI, Eurocode 2 and CSA models to predict the shear strength was validated using a data base of 479 specimens collected from literature. The proposed model has proven to yield accurate and consistent results in comparison with ACI, Eurocode 2 and CSA sectional models. Furthermore, the proposed model has shown that the effective depth of the beam has either very little or no influence on the shear strength. Finally, a parametric study was also conducted to study the influence of the various parameters on the shear strength.

Use of waste foundry sand with multiscale modeling in concrete

This paper represents the study of mechanical properties of concrete by utilizing the waste foundry sand (WFS) as a replacement material in the production of concrete. Waste foundry sand is obtained from the industries where aluminum is cast, which is a sand used for the purpose of casting the moulds. WFS are used in different ratios such as 20%, 25% and 30% and also several investigations were carried out to determine the compressive strength, elastic modulus and Poisson’s ratio with the help of the Bazant–Baweja (B3 model) using multiscale modeling at each level, American Concrete Institute (ACI model) and Indian Standards (IS method) to know the behavior of concrete. The proposed method does not require any prior information with respect to the mechanical properties of bond, for instance, modulus of elasticity or compressive strength. The test results related to the proposed model for elastic modulus at the level of concrete bearing a value of 36.92 kN/mm2 and 37.78 kN/mm2 for the water-to-cement ratio (w/c) 0.4 and 0.5, respectively. The test results produced that the strength of concrete up to 30% was relatively close when compared with control mixture (CM) for w/c-0.4, with an average increase of about 1.9%. Similarly, 20% of WFS usage had a variation of 6.1% when compared with the CM for w/c-0.5. The further strength reduction in WFS is recognized due to the fineness of WFS and also with the presence of dusty particles. From the results obtained, it is concluded that WFS can be replaced with 30% and 20% for 0.4 and 0.5 w/c, respectively, with an effective manner in the production of concrete.

Mechanical model for punching shear capacity of rectangular slab‐column connections

This paper investigates the punching behavior of reinforced concrete flat slabs supported on rectangular columns under concentric loading. Based on the critical shear crack theory, a new model is proposed to determine the punching shear strength of slabs. In this model, a rectangular slab is replaced with an elliptical surface with the same area. The efficiency of the model is validated through comparisons made with experimental studies in the literature. Furthermore, results are compared with three different codes, namely, ACI, Eurocode 2, and FIB Model Code 2010. Finally, an alternative approach is introduced to facilitate the calculation of the punching shear capacity of slabs with column rectangularity considerations. For the experimental tests available in the literature, good shear strength predictions were obtained by the two proposed models.

Coupled effect of coarse aggregate and micro-silica on the relation between strength and elasticity of high performance concrete

This paper examines the relation between strength and elastic modulus of high performance concrete (HPC) tailored from various heavy and normal weight aggregates coupled with the effect of micro-silica as a supplementary cementitious material (SCM). Elastic modulus of concrete is an important mechanical property and plays an important role for the calculation of deformations in the structural components. Experimentation was conducted in precise laboratory environment and all other parameters were kept constant in the mixtures. This investigation was prompted to supply the construction industry with appropriate information on how specific properties of HPC mixtures can be improved using local normal and heavy weight aggregates and incorporating supplementary cementitious materials. In other words, this paper will encourage the local aggregate consumption in mega projects that to be constructed for special purposes. In this investigation, dissimilar types of normal and heavy weight coarse aggregates were used. It was found that it is worthy to study experimentally the relation between strength and MOE of HPC when different types of coarse aggregates are used for an indicated HPC mixture with a corresponding combination of supplementary cementitious material. The comparison of experiment results with the ACI prediction models showed that the models should be enhanced for accurate prediction for the effect of aggregate type with and without the use of micro-silica as supplementary cementitious material. An assessment of the need for an aggregate and micro-silica based modification to the ACI models is also proposed. The experimental work conducted in this investigation confirmed that the type of aggregate and its combination with a supplementary cementitious material would have important influence on the HPC characteristics. Hence, the use of appropriate values for the strength-MOE relation for a HPC mixture based on the nature of used aggregates and SCM is recommended. However, such values might be not available in some cases, if so the experimental trend lines presented in this study can be used to calculate them.

Effect of a tissue selective estrogen complex on breast cancer: Role of unique properties of conjugated equine estrogen.

The Women's Health Initiative studies reported that the menopausal hormone therapy (MHT) regimen containing conjugated equine estrogen (CEE) and medroxyprogesterone acetate increased, whereas CEE alone reduced breast cancer incidence. These observations suggest the possibility that CEE might exert unique actions on breast and also suggest the need to eliminate the progestogen from MHT regimens. A MHT regimen called a tissue selective estrogen complex (TSEC), containing CEE plus bazedoxifene (BZA), to avoid the need for a progestogen, was developed and FDA approved. Our study addressed two questions regarding this TSEC: (i) whether CEE exert effects on breast cancer which differ from those of estradiol (E2 ) and (ii) whether BZA antagonize the effects of E2 and CEE on breast cancer? Two rodent models (NMU and ACI) were used to compare the effect of CEE with E2 on mammary tumor formation, proliferation and apoptosis. In both the NMU and ACI models, E2 significantly increased tumor incidence and multiplicity whereas in striking contrast CEE did not, even though the estrogenic effects of CEE and E2 on uterine weight were identical. Mechanistically E2 blocked whereas CEE stimulated apoptosis (cleaved caspase-3) in ACI animals and only E2 stimulated proliferation (Ki67). BZA exerted highly potent anti-estrogenic effects on tumors by completely blocking palpable tumor formation. These data suggest that the CEE/BZA TSEC may be a safer, breast-antagonistic, MHT agent for women and might have potential to prevent breast cancer while relieving menopausal symptoms.

Abstract 246: Rescuing an Acquired Cardiac Retinoic Acid Deficiency Prevents Hypertrophy and Sudden Cardiac Death in a Pressure Overload/Chronic Catecholamine Model of Hypertrophy and Heart Failure

Introduction: Recently, we have investigated a pressure-overload/chronic catecholamine guinea pig model (ACi) of cardiac hypertrophy (HYP) and HF with the unique features of acquired long QT syndrome and sudden cardiac death (SCD) by quantitative global-scale proteomics using isobaric tags for relative and absolute quantitation. Hypothesis: By compiling proteins altered significantly both compensated HYP and HF, it may be possible to identify novel early contributors to pressure overload- induced HF pathogenesis. Results: Pathway mapping of proteins differentially regulated in HYP that were also changed in HF (p<0.05 in both HYP and HF) revealed altered “retinoate biosynthesis” (p<0.01) and “RAR Activation” (p<0.05), suggesting that guinea pig HYP &HF might be related to impaired Vitamin A metabolism, specifically, to a deficit in the bioactive metabolite, all-trans retinoic acid. Causal Regulator Analysis indicated that coordinate regulation of ATRA-responsive proteins was unlikely to have occurred by chance (p=1.88x10 -11 ) and that the ATRA program was downregulated (z-score<-1.2). ATRA deficit would attenuate transcriptional programs that control fatty acid oxidation, excitation/contraction-coupling, contraction, and antioxidant defense - all of which were decreased in heart failure. Metabolomic profiling by mass spectrometry showed that ATRA, alone among the resident cardiac retinoids, was downregulated in HYP and HF (Down 32% & 33% respectively p<0.05). Secondly, the specific agonist of RXR signaling, 9-cis RA, is not present in adult guinea pig hearts. Proteome and transcriptome data indicate that the ATRA deficit stems from downregulation of retinaldehyde dehydrogenase 1 (RALDH1) by 23% in HYP and 39% in HF (p<0.01 each). Treatment with ATRA (2mg/kg/day) mitigated heart weight/tibia length (ACi: 0.71 , ACi + ATRA: 0.57; p<0.01), improved fractional shortening (27.4% vs 37.5%, p<0.01) and ejection fraction (50.4% vs. 64.8%, p<0.01). Preliminary studies indicate that ATRA treatment also reduces the incidence of sudden cardiac death (55% vs 15% (p<0.01)) in the guinea pig ACi model. Conclusion: The data support a causal role for ATRA deficiency in the pathogenesis of pressure overload-induced HF and susceptibility to SCD.

Deformation of concrete made with crushed recycled glass cullet fine aggregate

Only around a third of waste glass is used in the production of new glass products, so alternative applications are needed to deal with the huge amount remaining. At the same time there is a growing pressure to reduce the environmental impact of concrete production, and use of recycled and secondary aggregates offers one of the best solutions. Deformation properties, in the form of elastic, creep and shrinkage strains of concrete made with glass cullet as fine aggregate are examined. The modulus of elasticity of concrete is increased by 10·5% when glass cullet fine aggregate of a similar grading to natural fine aggregate is used. Its inclusion in concrete does not change the relationship between strength and modulus of elasticity. The creep of glass cullet fine aggregate concrete is suggested to be similar to that of natural fine aggregate concrete. The shrinkage of concrete decreases at a decreasing rate with increasing glass cullet fine aggregate content, giving 16% reduction at 100% replacement of natural fine aggregate. The restraint effect provided by glass cullet fine aggregate in concrete can be affected by the strength of the concrete and the water absorption of the fine aggregate used. The estimations of deformation of concrete containing glass cullet fine aggregate using Eurocode and ACI models are also described.

Punching Shear Resistance of High Strength GFRP Reinforced Concrete Flat Slabs

This study program has been arranged to test the behavior of punching shear for concrete slabs reinforced by an embedded glass fiber reinforced polymer (GFRP) reinforcements. However, the shear resistance of concrete members in general and especially punching shear of two-way RC slabs, reinforced by GFRP bars has not yet been fully investigated. Seven decades ago, many researches have been carried out on punching shear resistance of slabs reinforced by conventional steel and several design methods were created. However, these methods can be not easily applied to FRP-reinforced concrete slabs due to the difference in mechanical properties between (FRP) and steel reinforcement. sixteen specimens are to be cast in lab within two categories of reinforcements such as GFRP and equivalent steel reinforcements. In addition, based on experimental data obtained from the author’s study and ACI model, the paper performed an evaluation of accuracy of proposed model. The results from the evaluation show that the ACI-formula gave inaccurate results with a large scatter in comparison with the test results of this study. A new design formula can be proposed for more accurate estimation of punching shear resistance of (GFRP) specimens.

Analysis of R/C frames considering cracking effect and plastic hinge formation

The design of reinforced concrete buildings must satisfy the serviceability stiffness criteria in terms of maximum lateral deflections and inter story drift in order to prevent both structural and non-structural damages. Consideration of plastic hinge formation is also important to obtain accurate failure mechanism and ultimate strength of reinforced concrete frames. In the present study, an iterative procedure has been developed for the analysis of reinforced concrete frames with cracked elements and consideration of plastic hinge formation. The ACI and probability-based effective stiffness models are used for the effective moment of inertia of cracked members. Shear deformation effect is also considered, and the variation of shear stiffness due to cracking is evaluated by reduced shear stiffness models available in the literature. The analytical procedure has been demonstrated through the application to three reinforced concrete frame examples available in the literature. It has been shown that the iterative analytical procedure can provide accurate and efficient predictions of deflections and ultimate strength of the frames studied under lateral and vertical loads. The proposed procedure is also efficient from the viewpoint of computational time and convergence rate. The developed technique was able to accurately predict the locations and sequential development of plastic hinges in frames. The results also show that shear deformation can contribute significantly to frame deflections.

Optimal adjustment of ACI formula for shrinkage of concrete containing pozzolans

Very few models have been developed to estimate shrinkage of concrete containing pozzolans, and most existing models (particularly the ACI model) are not calibrated with pozzolanic concrete. This paper presents an improvement of the ACI model for shrinkage of concrete containing three types of pozzolans including silica fume (SF), fly ash (FA), and slag (SL). A comprehensive database is collected from the literature to cover a wide range of mixture components and mix proportions. In particular, to capture the effect of the dosage and type of each pozzolan, the time function in the ACI model is modified and a new correction factor associated with compressive strength is added. The model parameters in the modified time function and the new correction factor are assessed using a computational intelligence method called particle swarm optimization. The results of several statistical indicators show better prediction performance for the modified ACI model (M-ACI) than the original ACI formula.

Flexural performance of FRP-reinforced concrete encased steel composite beams

This paper presents a numerical method for estimating the curvature, deflection and moment capacity of FRP reinforced concrete encased steel composite beams (FRP-RCS). A sectional analysis is first carried out to predict the moment-curvature relationship from which beam deflection and moment capacity are then calculated. Comparisons between theoretical and experimental results of tests conducted elsewhere show that the proposed numerical technique can accurately predict moment capacity and deflection of FRPRCS composite beam. The numerical results also indicated that beam ductility and stiffness are improved when encased steel is added to FRP reinforced concrete beams. ACI, ISIS and Bischoff models for deflection prediction compared well at low load, however, significantly underestimated the experimental results for high load levels.

Shear strength of RC beams without web reinforcement

Due to the complexities of the mechanics of shear failure in reinforced concrete (RC) members, most current approaches for predicting shear strength are mainly empirical. Being empirical, these approaches do not physically explain the shear failure mechanism seen in practice and consequently should only be used within the bounds of the testing regimes from which they were derived; this restricts their application to innovative materials such as fibre-reinforced polymer RC beams or those with high-performance concrete. In this paper, a numerical mechanics-based segmental approach for the shear failure of RC beams with any type of reinforcement and concrete is developed; from the mechanics of the segmental approach, simplifications are made to develop closed form solutions and the resulting design equations are compared to a database of 626 steel-reinforced specimens. Further comparisons to the predictions made by the ACI, AS 3600 and FIB Model Code 2010 approaches show that the proposed approach offers improved accuracy and a reduction in scatter.

Combined Effect of Silica Fume and Steel Fiber on Modulus of Elasticity of High Performance Concrete

Concrete elastic modulus is a basic property required for the appropriatepredicting of its basic behavior and for its correct implementation in a variety ofconstructional and engineering applications. This study presents an experimental and analytical evaluation of elastic modulus of high performance concretes (HPC) produced bysteel fiber and silica fume. The aim of this study is to develop the elastic modulus propertyof HPC and to show the applicability of ACI models to predict the elastic modulus of HPC from compressive strength. Four volume fractions of steel fiber with an aspect ratio (fiber length/ fiber diameter) of 60 were used (0, 0.5, 1.0, and 2.0 %). Incorporations of silica fume into the concrete were 0% and 15% by weight as a cement replacement. Water/cement ratio was ranged (0.28-0.4) with different amount of superplasticizer, and the reference slump was 170 mm. Both compressive and elastic modulus tests were made on hardened concretes reinforced with steel fibers and then compared with control specimens at 14 and 28 days. The results showed that the presence of silica fume enhanced the compressive strength and modulus of elasticity of evaluated concretes. In addition, adding steel fiber slightly increased both strength and modulus of elasticity values. Also, results showed that the elastic modulus of HPC is relative to the compressive strength, the ACI 318 expression is predicting elastic modulus of HPC and HPC-SF superior than ACI 363, but ACI 363 equation seems to be better in prediction modulus of elasticity of HPC-SF0.5S, HPC-F1.0S, and HPC-SF2.0S in comparison with ACI 318.

Separation Method of Strain Caused by Concrete Shrinkage and Creep in Bridge Health Monitoring

The strain caused by concrete shrinkage and creep is separated through the field measurement data in this paper. Then D62 model and ACI model of finite element model is established to predict shrinkage and creep. Compared with the measured data, the feasibility and practicability of these two models can be proved.

Shear Behavior of Reinforced Concrete Deep Beams with Various Horizontal to Vertical Reinforcements and Shear Span-to-Effective Depth Ratios

This paper presents the test results on the shear behavior of reinforced concrete deep beams with six steel reinforcement configurations. They were designed in accordance with the method given in the ACI 318-11. The specimens were subjected to the single concentrated loading at mid-span. The horizontal to vertical reinforcement ratios and shear span-to-effective depth ratios were the variables studied. The shear span-to-effective depth ratios of the beam specimen were between 1.5 to 2.0. The strut-and-tie model was used for the analysis. The test results indicated that the first diagonal cracking load and the failure mode were controlled by the horizontal to vertical reinforcement ratios and the shear span-to-depth ratios. The tests consistently gave the strength values slightly less than those calculated by using the ACI model. A modified ACI model for strut-and-tie was thus proposed and was found to accurately fit the experimental results.

Kompozitinės Armatūros Inkaravimo Betone Ypatumai

This article analyzes the basic problems of the anchorage of non-metallic reinforcement for concrete and reviews calculation methods of anchorage length using ACI, STR, JSCE and fib Model Code 2010. The paper presents a comparison of experimental (Benmokrane et al. 2003) and theoretical results and studies the major types of experimental tests to determine the bond strength of FRP reinforcing bars. The anchorage length of continuous fiber reinforcement (non-metallic reinforcement bars) is calculated using diff erent expressions proposed in codes and recommendations, thus providing with particular results. The article also shows how the anchorage length of a reinforcing bar is influenced by mechanical properties of reinforcement and concrete, concrete cover and the diameter of the reinforcing bar. Experimental results are compared with theoretically obtained values referring to codes and recommendations. A scatter of results is 3.67-10.18. It was found, that the anchorage length of the carbon fiber reinforced polymer (CFRP) bar calculated by ACI, STR, JSCE and MC increases in the number of times an increase in bar diameter. It has been stated, that anchorage length decreases by 1,44 and 1,71 when the compression strength of concrete increases by 2 and 4. Theoretical calculations have revealed that depending on a bar diameter, in order to minimize the anchorage length of non – metallic reinforcement, the use of the concrete cover higher than 3 db is not feasible. Moreover, when using conventional steel for concrete reinforcement, anchorage length is 3 times less than that of a concrete member with carbon fiber reinforced polymer (CFRP) reinforcement and 2 times less than using basalt fiber reinforced polymer (BFRP) reinforcement. Calculation methodology for the anchorage length of a steel reinforcing bar can be used for calculating the anchorage length of non-metallic reinforcement. However, individual coefficients of diff erent FRP reinforcement must be applied to determine environmental factors and temperature of mechanical properties of non-metallic reinforcement. The values of coefficients must be determined conducting experimental tests.

Aging coefficient, creep coefficient and extrapolating aging coefficient from short term test for sealed concrete

Aging coefficient and creep coefficient are important parameters for creep analysis of any structure. With the aim to obtain those parameters, an experimental investigation is carried out on sealed concrete. Altogether ten specimens were tested, out of which four were for creep, two for shrinkage and remaining four for relaxation test. A year of relaxation test and two years of creep test results were analyzed to compute aging coefficient and creep coefficient. From regression analysis of observed and calculated aging coefficient using formula of Bazant and Kim, modification for aging coefficient is performed and extrapolation equations are generated. Instead of ACI model, B3 model has been used to obtain compliance function as the parameters of B3 model seems more relevant to creep mechanism of concrete compared to that of ACI model.

Three-Dimensional Analysis of Tall Reinforced Concrete Buildings with Nonlinear Cracking Effects#

In this study, a computer program based on the iterative analytical procedure has been developed for the three-dimensional analysis of reinforced concrete frames with beam, column and shear-wall elements in cracked state. ACI and probability-based effective stiffness models are used for the effective moment of inertia of the cracked members. In the analysis, shear deformation effects are also taken into account, and the variation of the shear rigidity due to cracking is considered by employing the reduced shear stiffness models available in the literature. The computer program is based on an iterative procedure which is subsequently verified experimentally through a reinforced concrete wall-frame test. The effectiveness of the analytical procedure is also illustrated through a practical three-dimensional reinforced concrete shear wall frame example. The iterative analytical procedure can provide an accurate and efficient prediction of deflections of reinforced concrete structures due to cracking under service loads. The main advantage of the proposed procedure is that the variations in the flexural stiffness of each member in the reinforced concrete structures can be observed explicitly.

Required Guardband for Coexisting LTE/FDD Systems Obtained by Accurate Analysis Of Adjacent Channel Interference

Adjacent channel interference (ACI) can cause serious performance degradation in certain frequency bands when multiple LTE systems are deployed near each other. This paper proposes a more accurate ACI model to calculate the interference power from the adjacent system. A dynamic system level simulator is used to show and analyze the throughput loss as a function of ACI ratio (ACIR) at 2000 MHz. Effective ACIR to guardband mapping functions are derived to determine a more accurate guardband for coexisting LTE systems to satisfy the throughput loss requirement.