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عنوان فارسی مقاله:
مدل انتشار فشار آب حفره ای برای پیش بینی فشار قالب اعمال شده توسط بتن مخلوط
عنوان انگلیسی مقاله:
A pore water pressure diffusion model to predict formwork pressure exerted by freshly mixed concrete
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Accidents in the process of concrete placement reportedly cause heavy casualties during the construction of concrete structures. For example, two major accidents in Korea were reported in 2015. Each case led to approximately 10 laborer casualties. These accidents were triggered by the collapse of a roof-slab form or bridge-deck form when the concrete was placed. Questions are being asked regarding the safety of form and shoring systems. The formwork pressure exerted by freshly mixed concrete is one of the most important considerations in the design of form and shoring systems. Introducing cast-in-place self-consolidating concrete (SCC) has led to quantitative evaluations and analyses of the form pressure since the early 2000s. The conventional formula for the form pressure, such as the ACI 327 guideline for formwork [1,2], hardly considers the fluidity of self-consolidating concrete. A higher level of form pressure load was then proposed for self-consolidating concrete in the DIN code [3], where the placement rate was revealed as the most influential parameter [4,5]. The current update reflected a variety of experimental measurement on the form pressure exerted by SCC [6e8]. Understanding the lateral pressure response and its decay was accomplished with several models such as a phenomenological model based on the pressure response [9e11], the increase of thixotropic resistance [12e14], or pore water pressure [15,16]. The hypotheses on intrinsic effect of freshly mixed concrete could be categorized as follows: (1) the cohesion-friction model, such as the Mohr-Coulomb theory and Rowe's theory [17,18]; (2) the rheological evaluation based on the thixotropic evolution of the yield stress [19,20]; and (3) decay of the pore water pressure in cement-based materials [21e23]. Still, the mechanism of form pressure decay requires additional study. On the other hand, the previously described accidents also indicate the effect of formwork materials, an extrinsic factor. The old-fashioned wood gang-form has been replaced by steel or polymeric composite system-forms for the efficiency of formwork installation in construction sites. Note that the conventional ACI formula was based on the traditional formwork. The change of formwork material affects the form pressure. A limited number of studies reported the evaluation of the effect of the form friction [24,25]. The variance on form pressure was also recorded according to the form surface material [26]. In these days, the efficient system-form composed of polymeric composites or steel isolates the freshly placed concrete inside it and almost flawlessly prevents the leakage of bleed water. The bleedwaterproofed form system presumably causes excess pore waterpressure on freshly mixed concrete, which results in a higher form pressure. The diffusion of pore water pressure in freshly mixed concrete addresses the decay of form pressure. In this study, a comprehensive model based on decay of the pore water pressure is proposed to analyze the effect of formwork materials. Applying the Biot theory of poroelasticity allows us to formulate the diffusion of pore water pressure and then predict the form pressure exerted by the freshly mixed concrete. Both normally vibrated concrete (NVC) and SCC were consistently evaluated under the same formulation. A mockup test considering a 3.4-m high column were performed to verify the proposed model.
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کلمات کلیدی:
[PDF]Portable Pressure Device to Evaluate Lateral Formwork Pressure ... https://www.researchgate.net/...Pressure...Formwork_Pressure_Exerted...Concrete/.../5... static pressure has hindered the acceptance of SCC in the ready-mix concrete as ... pressure exerted by fresh concrete using two strain gauge plates. Full bridge ... A pore water pressure diffusion model to predict formwork pressure ... iranarze.ir/wp-content/uploads/2016/11/E2875.pdf Sep 29, 2016 - The formwork pressure exerted by freshly mixed concrete is one of the most important ... The diffusion of pore water pressure in freshly mixed. [PDF]Study of the Lateral Pressure of Fresh Concrete as Related to the ... https://ntl.bts.gov/lib/60000/60500/60584/308-1F-CTR.pdf by JB Bernal - 1983 - Cited by 6 - Related articles diameter, circular steel formwork and instrumented on the sides to measure the pressure ... different distributions of lateral pressure can be exerted by concrete. ..... water. Properly mixed fresh concrete forms a mass with a more or less uniform. Portable Pressure Device to Evaluate Lateral Formwork Pressure ... ascelibrary.org/doi/abs/10.1061/(ASCE)MT.1943-5533.0000537 by AF Omran - 2012 - Cited by 7 - Related articles ... Device to Evaluate Lateral Formwork Pressure Exerted by Fresh Concrete ... are used to validate the pressure device, including placement rate as well as mix ... [PDF]In-situ measurement of formwork pressures generated by ... - WIT Press www.witpress.com/Secure/elibrary/papers/CMEM07/CMEM07083FU1.pdf by MM Giammatteo - 2007 - Cited by 4 - Related articles In this paper an experimental study on formwork pressure exerted by SCC ... dimension and shape of the aggregate, consistency of fresh concrete, setting ... diaphragm due to the flow of freshly mixed materials, indeed, is not reversible,. [PDF]State-of-the-Art Review of Form Pressure Exerted by Self ... www.concretesdc.org/projects/sccfinalreport/finalreportsccformpressure.pdf THE NATIONAL READY-MIX CONCRETE RESEARCH FOUNDATION and. THE STRATEGIC DEVELOPMENT .... 2.4 Fresh concrete properties . ..... PROPERTIES OF SCC AFFECTING FORMWORK PRESSURE 129 · 4.1 Objectives . [PDF]Tightness requirements for SCC formwork - WTCB www.wtcb.be/?dtype=research&doc=2016_PVI...SCC2016...formwork... by T Cools - Related articles when placing ready-mixed self-compacting concrete (SCC). These sealing ... lateral pressure exerted by fresh concrete on vertical formwork panels, one of the.