• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.419-426
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• 2010

This paper discusses a series of experiments including material improvement in order to ensure quality of grouting for the post-tensioned structure. In presstressed concrete, grouting refers to the construction procedure of filling empty space of duct enclosing the prestress tendons using cementitious material, To date, adequate quality control of the grouting has not been established in Korea because the relationship between the grouting and durability of post-tensioned structure is not well-recognized. The Korean standard does not consider the important material characteristic, wick effect, which is caused by tendons in the ducts, and furthermore current standard testing method does not quantify reasonable material segregation. As a result, the grout material, which satisfies the current material standards, may well exhibit excessive bleeding of water or shrinkage during construction. In this study, international codes and standards related to grouting were surveyed. The mix proportions of the constituents and novel admixtures were suggested to meet equivalently with these standards. Performance of this enhanced grout was compared with common domestic grouts using the international standard testing method. A series of mock-up specimens considering geometry of PC beam was constructed and grout flow pattern was observed as the grout was injected. It was observed that the grouting performance was highly influenced by material properties and filling characteristic can be varied depending on geometry of ducts.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.661-668
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• 2009

Effective beam width model(EBWM) has been used for analysis of post-tensioned(PT) flat plate slab frames under lateral loads. The accuracy of this model in predicting lateral drifts and unbalanced moments strongly depends on the estimated effective stiffness of PT flat plate slabs. As moments on the slab due to lateral loads increases, cracks occur which leads to stiffness reduction in slabs. For analyzing PT flat plate slab structure under lateral loads with good precision, reduction in slab stiffness has to be accurately estimated for EBWM. For this purpose, this study collected test results of PT flat plate system conducted by former researches. And this study reduced the width of slab so that the stiffness of the EBWM converged into the lateral stiffness of each test specimens by trial and error. By conducting nonlinear regression analysis using the stiffness ratio of the reduced width of slab to the effective width of EBWM with respect to the level of slab moments, an equation for calculating stiffness reduction factor for slab is proposed. For verifying the accuracy of the proposed equation, this study compared with the test result of the PT flat plate frame. It is shown that the EBWM with the proposed equation predicts the actual stiffness of the PT specimen which varied according to the level of applied moment.

• Computers and Concrete
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• v.5 no.6
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• pp.525-544
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• 2008

In this research, the self-centering effect in precast and prestressed reinforced concrete structures was investigated experimentally. The reinforced concrete beams and columns were precast and connected by post-tensioning tendons passing through the center of the beams as well as the panel zone of the connections. Three beam-to-interior-column connections were constructed to investigate parameters such as beam to column interfaces (steel on steel or plastic on plastic), energy dissipating devices (unbonded buckling restrained steel bars or steel angles) and the spacing of hoops in the panel zone. In addition to the self-centering effect, the shear strength in the panel zone of interior column connections was experimentally and theoretically evaluated, since the panel zone designed by current code provisions may not be conservative enough to resist the panel shear increased by the post-tensioning force.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.821-826
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• 2001

This paper presents four types of strut-tie model design approaches of structural concrete through the anchorage zone design of a post-tensioned concrete I-beam. The differences and distinctive feature of each approach in terms of structural type of selected strut-tie model, external force acting on strut-tie model, effective strength of concrete strut, and strut-tie model design procedure are analyzed and compared. The outcomes of present study enable structural designers to understand the merits and demerits of each strut-tie model design approach, and thus to conduct reasonable and accurate design of structural concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.241-246
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• 2000

In the strut-tie model design of structural concrete, the importance of the effective strength of concrete strut has been overlooked by many practitioners. The authors believe that the effective strength of concrete strut is an important factor not only in determining steel tie forces but also in verifying the nodal zone strength and geometric compatibility condition of a selected strut-tie model. This study evaluate the effect of the effective strength of concrete strut on structural concrete design by applying the different effective strut strengths to the strut-tie model design of a post-tensioned anchorage zone and a continuous concrete deep beam.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.888-895
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• 2000

As conventional grouting materials for the sheath such as cement slurry or cement-mortar are mixed and pumped in site, those harden with bleeding or shrinkage and meets low compressive strength. Also the materials haven't always same cements, sand size distributions, additives in site, so those materials have unstable quality properties. We have studies on ready-mixed-mortar for grouting pretensioned or post-tensioned cables and rods to encapsulate the steel so that we have developed a formulation of specially selected, flowable, shrinkage-compensating materials.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.269-272
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• 2006

The anchorage zone of prestressed concrete members is a critical region where a large concentrated force due to prestressing by tendons is introduced. In this study, the ACI, AASHTO LRFD, CEB-FIP design criteria and the nonlinear strut-tie model approach are applied to the ultimate strength analysis of simple anchorage zones of 18 post-tensioned concrete members tested to failure. From the result of ultimate strength analysis, the advantages and disadvantages of each method are compared and discussed.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.7-14
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• 2011

The numerical analyses were performed to investigate the curling behavior of the post-tensioned prestressed concrete approach slab (PTAS) under environmental loads. A technique to include properly the boundary conditions of one end of PTAS that was connected to the bridge abutment using hinges was proposed for the numerical model. The applicability of a simplified model not having hunches was also investigated. By using the developed models, the curling behavior of PTAS was analyzed when the foundation settlement occurred. The analysis results showed that the maximum tensile stress obtained from the simplified model involving a simplified hinge connection was very closed to that obtained from a rigorous model. When the slab curled up, the maximum tensile stress occurred in the model including no foundation settlement, but when the slab curled down, the maximum stress occurred in the model including partial settlement of the foundation. Therefore, the design of PTAS should be performed considering those maximum tensile stresses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6898-6905
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• 2014

A stress ribbon bridge is a PSC structure that behaves as a reverse arch structure due to post-tensioned thin deck of the catenary type. In foreign countries, the stress ribbon bridge is recognized as the minimum destruction of nature and beautiful bridge, and has many construction examples as pedestrian and car bridges. On the other hand, there have been few studies in Korea. In this study, the FE Analysis model was established for different construction stages considering the nonlinear and time-dependent behaviors. The FE model was verified by a comparison with the numerical results and the behavior was analyzed for the different construction stages.

• Structural Engineering and Mechanics
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• v.82 no.5
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• pp.595-609
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• 2022

Prestressed composite steel-concrete beams are still a technology restricted to repair sites of large-scale structures and spans. One of the reasons for that is the absence of standard frameworks and publications regarding their design and implementation. In addition, the primary normative codes do not address this subject directly, which might be related to a scarcity of papers indicating methods of design that would align the two technics, composite beams and external prestressing. In this context, this paper proposes methods to analyze the sizing of prestressed composite beams submitted to pre-tension and post-tension with a straight or polynomial layout cable. This inquiry inspected a hundred and twenty models of prestressed composite beams according to its prestressing technology and the eccentricity and value of the prestressing force. The evaluation also included the ratio between span and height of the steel profile, thickness and typology of the concrete slab, and layout of the prestressing cables. As for the results, it was observed that the eccentricity of the prestressing force doesn't significantly influence the bending resistance. In prestressed composite beams subjected to a sagging moment, the ratio L/d can reach 35 and 30 for steel-concrete composite slabs and solid concrete slabs, respectively. Considering the negative bending moment resistance, the value of the L/d ratio must be less than or equal to 25, regardless of the type of slab. When it comes to the value of the prestressing force, a variation greater than 10% causes a 2.6% increase in the positive bending moment resistance and a 4% decrease in the negative bending moment resistance. The pre-tensioned composite beams showed a superior response to flexural-compression and excessive compression limit states than the post-tensioned ones.