كليدواژه :
عرشه پيش ساخته ي قطعه اي , بتن پس تنيده , زلزله ي قائم , درز , نزديك گسل
چكيده فارسي :
به دليل مزاياي فوق العاده ي پل هاي پيش ساخته ي قطعه اي از جمله سرعت ساخت و ساز بالا و عدم نياز به انسداد جريان ترافيك در مناطق شهري، استفاده از آن ها در جهان در حال گسترش است، ولي استفاده از آن ها در مناطق لرزه خيز به دليل عدم وجود اطلاعات كافي از پاسخ ديناميكي شان با نگراني هايي همراه است. با توجه به پيش ساخته بودن اين نوع پل ها و جهت اجراي سريع تر، اتصال و پيوستگي قطعات با يكديگر از طريق تنيدگي صورت مي گيرد بنابراين ا انتظار مي رود تحت تحريك زلزله ي قائم، رفتار روسازه به خصوص در پل هايي كه عرشه به صورت دهانه هاي ساده و مجزا بر روي پايه ها قرار مي گيرند، متاثر از عملكرد درزها باشد. در مطالعه ي حاضر سعي شده است تاثير زلزله ي قائم بر عرشه ي اين پل ها در مناطق نزديك و دور از گسل با مدل سازي يك پل نمونه مورد مطالعه قرار گيرد و ميزان خسارت زلزله ي قائم بر عرشه ي پل ها در سطوح مختلف زلزله بررسي شده و ارزيابي گردد. نتايج نشان داد پاسخ اين پل ها و درزها مي تواند بسيار متاثر از مولفه ي قائم باشد، به گونه اي كه با توجه به نتايج مربوط به ميانگين تغيير مكان درزها، بازشدگي محتمل ترين خسارت ناشي از مولفه ي قائم زلزله است.
چكيده لاتين :
Precast segmental construction methods can decrease bridge construction costs by reducing construction time while the quality control criteria are satisfied. In addition, the absence of scaffold can minimize traffic congestion and environmental impacts. Because of these great advantages, application of precast segmental bridges is increasing in the world. However, lack of reliable knowledge about the dynamic response of these bridges under seismic loads has limited their application in high seismicity areas. Combination of the precast construction with the post-tensioning contact on segment joints, may result in expecting a defeated behavior of superstructure due to earthquake excitation. This may happen especially in case of vertical components, which may harm the joints operation in the presence of long-term loads. This issue is very probable in non-continuous post-tensioned bridges. The present paper aims to investigate the effects of vertical earthquake on bridge superstructure in near-fault regions by studying a sample model and obtaining structural response including joints response and their openings, force-displacement response of the system, stress and strain in concrete and cables, and their level of nonlinearity. The research shows that segment joints can undergo very large rotations that open up gaps in the superstructure; Whereas, primary seismic concerns - regarding segmental construction - focus on the behavior of the joints between segments, and no mild reinforcement crosses trough them. The lack of reinforcement across segment joints may result in an increased rate of construction. Yet, it creates inherent regions of weakness that are susceptible to facing crack initiation and large localized rotations. At the first step of numerical modeling, specimens studied by Megally et al. [1-3] were modeled in OpenSees V2.4.4. The specimens discussed the regions with high moment and low shear (i.e. near mid-span).Using detailed 2D nonlinear time history analysis under a suite of ten near-field earthquake records, the effects of vertical motion on the joint response are quantifies. The prototype bridge structure - selected for this study- is a single-cell box girder bridge with a 50m span, consisted of sixteen 3-meters-long segments with non-bonded tendons constructed trough a span-by-span construction method. Segments of the superstructure are modelled using linear elastic frame type members, except for a region at the end of each segment which is discretized into several axial non-linear zero length springs. The springs are connected to the ends of the
superstructure beam elements through rigid body links. Results indicate that vertical components of earthquake can affect the response of these bridges, and segment-to-segment joints opening is very probable particularly at the midspan joints. Thus, superstructure may collapse under upward acceleration component due to the presence of the greater part of concrete on top flange and lack of tensile material on top of joints, or even the occurrence of sliding in elastomer caused by the decrease in effective weight. The joint compressive strain remains below the concrete spalling limit state, minimizing the damage and stiffness reduction of the superstructure. The cables remain in the
elastic range and all joints are closed after the earthquake, even in high seismic intensity levels, and the residual vertical displacements are negligible.
