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排序方式: 共有1525条查询结果,搜索用时 18 毫秒
41.
42.
Ultra-high performance concrete and fiber reinforced concrete: achieving strength and ductility without heat curing 总被引:5,自引:2,他引:3
Kay Wille Antoine E. Naaman Sherif El-Tawil Gustavo J. Parra-Montesinos 《Materials and Structures》2012,45(3):309-324
Ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHP-FRC) were introduced in the
mid 1990s. Special treatment, such as heat curing, pressure and/or extensive vibration, is often required in order to achieve
compressive strengths in excess of 150 MPa (22 ksi). This study focuses on the development of UHP-FRCs without any special
treatment and utilizing materials that are commercially available on the US market. Enhanced performance was accomplished
by optimizing the packing density of the cementitious matrix, using very high strength steel fibers, tailoring the geometry
of the fibers and optimizing the matrix-fiber interface properties. It is shown that addition of 1.5% deformed fibers by volume
results in a direct tensile strength of 13 MPa, which is 60% higher than comparable UHP-FRC with smooth steel fibers, and
a tensile strain at peak stress of 0.6%, which is about three times that for UHP-FRC with smooth fibers. Compressive strength
up to 292 MPa (42 ksi), tensile strength up to 37 MPa (5.4 ksi) and strain at peak stress up to 1.1% were also attained 28 days
after casting by using up to 8% volume fraction of high strength steel fibers and infiltrating them with the UHPC matrix. 相似文献
43.
44.
Steel fiber-reinforced ultra-high performance concrete (UHPC) is of increasing interest for use in precast prestressed concrete highway bridge girders due to its superior durability and the potential for reducing or eliminating shear reinforcement, due to the presence of steel fibers. However, the contributions of creep, and especially tensile creep, to long-term performance must be better understood to develop appropriate design specifications. Due to practical considerations, it is also of interest to investigate the influence of varying thermal treatment, including temperatures lower than those recommended by the manufacturer (i.e. 90 °C), on the creep of UHPC. In this 1-year study, the effects of three different thermal treatment regimes on tensile and compressive creep performance of UHPC are examined, with complementary characterization by nanoindentation and scanning electron microscopy. Results show that UHPC creeps phenomenologically differently in tension and compression. Both thermal treatments examined resulted in similar tensile creep behavior, suggesting that a lower temperature applied over a longer period could effectively cure UHPC. For the non-thermally cured UHPC, a 10 μm wide region observed at the fiber/matrix interface was characterized by reductions in elastic modulus as well as greater porosity and microcracking than the bulk paste. It is suggested that the quality of the fiber/matrix interface is a major contributor to the measured increased creep of non-thermally treated UHPC as compared to UHPC treated at 60 °C or 90 °C. 相似文献
45.
The use of glass fibre reinforced polyester composites raises many health and safety and environmental questions. One alternative is the development of high performance bio-based bio-composites with low environmental impact. Improved understanding of interfacial properties is essential to optimise the mechanical properties and durability of these materials, but so far few data are available. The present work describes the interfacial characterization of Flax fibre/Poly(lactic) acid (PLLA) system at the micro-scale using the microbond test. Different thermal treatments have been carried out (cooling rate and annealing) in order to evaluate the influence of matrix and interfacial morphologies as well as residual stress on interfacial properties. Micromechanical models have been used to determine the interfacial shear strength. When cooling rate is slow, improved interfacial properties are observed. 相似文献
46.
The post-yield response of steel beams is important in steel fabrication particularly for setting cambers. A commonly used cambering process known as “cold cambering” consists of bending the girder about its strong axis using single or dual symmetrically applied concentrated loads. This paper recasts available solutions for wide flange steel beams relating loads to permanent deformation in parametric form to determine the effect of cross-sectional geometry and load position on its post-yield response. Sensitivity analyses were then conducted to identify appropriate values of these key parameters and their impact on alternative cambering set-ups. This allows optimization of the cold cambering operation for single- and dual-load systems. The analysis shows that dual-load systems offer significant benefits over single-load systems as they develop the required camber profile at smaller loads without overstraining the steel section. The best results are obtained if the spacing between the two loads is kept within one-third to one-quarter of the span. 相似文献
47.
48.
Joseph Berry Tonio Buonassisi David A. Egger Gary Hodes Leeor Kronik Yueh‐Lin Loo Igor Lubomirsky Seth R. Marder Yitzhak Mastai Joel S. Miller David B. Mitzi Yaron Paz Andrew M. Rappe Ilan Riess Boris Rybtchinski Oscar Stafsudd Vladan Stevanovic Michael F. Toney David Zitoun Antoine Kahn David Ginley David Cahen 《Advanced materials (Deerfield Beach, Fla.)》2015,27(35):5102-5112
49.
50.
Andrea Kahn 《Journal of Architectural Education》2013,67(2):62-64
Sitelessness and loss of place suggest the instability of boundaries that otherwise sustain the legibility of public institutions. Such conditions negate conventional affinities between architecture, ceremonial urban space, monuments, and monumental sculpture. Nowadays, the theoretical basis for a relationship between these actors is in flux. This article takes up several different contemporary conceptions of public space and the public thing and employs them in an interpretation of two recent projects: Maya Lin's Vietnam Veterans Memorial and Richard Serra's ill-fated Tilted Arc. These projects embody changing conditions in the dialogue between art, architecture, and the city. 相似文献