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Control of Deflection in Concrete Structures ACI 435R-95 Reported by ACI Committee 435 This report presents a consolidated treatment of initial and time-dependent deflection of reinforced and prestressed concrete elements such as simple and continuous beams and one-way and two-way slab systems. It presents the state of the art in practice on deflection as well as analytical methods for computer use in deflection evaluation. The introductory chapter and four main chapters are relatively independent in content. Topics include “Deflection of Reinforced Concrete One-way Flexural Members,” “Deflection of Two-way Slab Systems,” and “Reducing Deflection of Concrete Members.” One or two detailed computational examples for evaluating the deflection of beams and two-way action slabs and plates are given at the end of Chapters 2, 3, and 4. These computations are in accordance with the current ACI- or PCI-accepted methods of design for deflection. Keywords: beams; camber; code; concrete; compressive strength; cracking; creep; curvature; deflection; high-strength concrete; loss of prestress; modulus of rupture; moments of inertia; plates; prestressing; pretensioned; post-tensioned; reducing deflection; reinforcement; serviceability; download ACI435.pdf

Considering Creep Parameters of Rock Mass to Evaluate the Necessity Thrust for Excavation in Squeezing Ground Original Article, D56 Mahdevari S, Bagherpour R. J. Civil Eng. Urban. 4(4): 370-377. 2014 ABSTRACT: There are a lot of complex problems involving a number of conflicting factors when planning a TBM drive in a squeezing ground. In this respect, numerical analyses represent a helpful decision aid. In this research, Beheshtabad water conveyance tunnel is introduced. Then, the geomechanical rock mass characteristics including time dependent parameters are determined for the 19th zone of Beheshtabad tunnel. Afterwards, the approaches to thrust evaluation and mitigation measures for thrust reduction are reviewed. Then the numerical simulation layout and the achieved results are investigated. According to these results, double and single shield Tunnel Boring Machines (TBM) might be utilized if 55 mm and 20 mm of over-boring in radius could be performed in the A&B and C geological units, respectively. Furthermore, over-boring quantity and shield length affect necessity thrust for excavation more than advance rate and the effectiveness of advance rate increment as a mitigation measure to thrust reduction is decreased by increasing the advance rate. Keywords: Beheshtabad tunnel, Creep, TBM, Thrust, 3D numerical simulation منبع: [Hidden Content] دانلود: [Hidden Content].,%204%20(4)%20370-377,%202014.pdf J. Civil Eng. Urban., 4 (4) 370-377, 2014.pdf

The Influence of Biofilm on the Mechanical Behavior of Sand S. W. Perkins,1 P. Gyr,2 and G. James3 REFERENCE: Perkins, S. W., Gyr, P., and James, G., “The Influence of Biofilm on the Mechanical Behavior of Sand,” Geotechnical Testing Journal, GTJODJ, Vol. 23, No. 3, September 2000, pp. 300–312. ABSTRACT: The growth of microbes on the surface of an object results in the formation of a biofilm, which in sand can lead to a reduction of hydraulic conductivity and can be used for groundwater containment and remediation. Sample preparation and testing techniques for triaxial and oedometer experiments were devised for the purpose of examining the influence of biofilm on the stress-straintime properties of Ottawa sand. Results have shown that biofilm has a negligible influence on the strength and stiffness of the sand but increases time-dependent creep deformation. An elasto-viscoplastic constitutive model was calibrated for biofilm and non-biofilm sand and implemented into a finite-element code for the purpose of predicting creep deformation of a slope and a foundation resting on level ground. Numerical simulations showed that additional creep behavior of the biofilm sand had a negligible influence on the behavior of these geotechnical engineering facilities. KEYWORDS: microbial bacteria, biofilm, biobarrier, sand, triaxial testing, oedometer testing, mechanical behavior, creep, constitutive modeling, finite-element modeling GTJ11052J.6514.pdf