AASHTO LRFD'ye göre betonarme bir köprünün tasarımı ve doğrusal olmayan statik itme yöntemi ile performansının belirlenmesi
Design of a reinforced concrete bridge as per AASHTO LRFD and determination of its performance using nonlinear static pushover method
Yazar: ŞAHİN BULUT
Danışman: PROF. DR. KUTLU DARILMAZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Bu tez çalışmasında, prefabrik öngerilmeli betonarme bir köprü, AASHTO LRFD 2017 yönetmeliğine göre tasarımı yapılmıştır. Ayrca, doğrusal olmayan statik itme analizi yöntemi ile tasarımı yapılan köprünün, DD-1 ve D-2 depremleri altındaki performansı incelenmiştir.
Çalışmanın birinci bölümünde, konuya giriş yapılarak tezin amacı açıklanmış ve bu tez çalışması esnasında yapılan literatür çalışmalarına değinilmiştir.
Çalışmanın ikinci bölümünde, köprünün betonarme tasarımı AASHTO LRFD 2017 yönetmeliğine göre yapılmıştır. Bu kapsamda, köprü boyutları ve köprüde kullanılacak malzeme özellikleri tanıtılmıştır. Köprüye gelecek sabit ve hareketli yükler belirlenip prefabrik kirişin öngerilme hesabı yapılarak tasarımı yapılmıştır. Ardından, köprünün bilgisayar modeli SAP2000 programında oluşturulmuştur. Programa tüm düşey, yatay ve deprem yükleri ile yönetmeliğin öngördüğü yük kombinasyonları tanımlanıp yapının analizi yapılmıştır. Analiz sonuçlarına göre başlık kirişi ve orta ayaklardaki kolonların betonarme tasarımları yapılmıştır.
Üçüncü bölümde, doğrusal olmayan analiz için genel bilgilendirme verilmiş ve kolonlarda oluşacak plastik mafsal boyu ve kolon kesitinin moment eğrilik ilişkileri açıklanmıştır. Ayrıca, doğrusal olmayan analizde kullanılacak olan DD-1 ve DD-2 depremlerine göre yatay elastik tasarım spektrumları verilmiştir. Ardından, KGM ile beraber Yüksel Proje'nin hazırladığı Karayolu ve Demiryolu Köprü ve Viyadükleri Mayıs ayı taslak raporuna göre performans hedeflerine göre elemanların plastik dönme sınırları belirlenmiştir. Son olarak,  doğrusal olmayan statik itme analizinin adımları verilmiştir.
Dördüncü bölümde, yapının doğrusal olmayan analizi yapılmış ve DD-1 ve DD-2 depremleri altında performansı belirlenmiştir. Bu kapsamda, SAP2000 programı kullanılarak köprünün statik itme ve kapasite eğrileri elde edilmiştir. Elde edilen kapasite eğrileri ile her iki deprem durumu yatay elastik tasarım spektrumları ile beraber incelenip köprünün performans noktası belirlenmiştir. Talep edilen yerdeğiştime miktarına kadar yapılan itme analizi sonucunda yapıda plastik mafsalların oluşmadığı görülmüştür. Plastik mafsalların oluşmamasından dolayı tasarımı yapılan köprü hem DD-1 hem de DD-2 depremi altında elastik davrandığı ve Kesintisiz Kullanım performans seviyesinde olduğu belirlenmiştir.
Beşinci bölümde, elde edilen sonuçlar özetlenmiş ve yorumlanmıştır.

Abstract:
In this study, a precast prestressed concrete bridge has been designed as per AASHTO LRFD 2017 specification. Additionally, performance behaviour under the DD-1 and D-2 earthquake loading cases have been investigated by nonlinear static pushover method for this bridge which was designed. 
The performance analysis of this structure has been determined as per relevant criteria stipulated by the May Draft Report for Railroad and Highway viaducts of General Directorate Highways, Head of Superstructures Departments. For the design and performans analysis of the structure SAP2000,  and for the moment analysis and interactive influence diagrammes XTRACT programmes have been used.  
In the first chapter of this study, the purpose of the thesis was briefed  and, literature studies related with the subject matter have been mentioned.   
In the second chapter of the study, structural concrete design of the bridge was carried out as per AASHTO LRFD 2017. Within this scope, structural dimensions and materials to be used were introduced. Live and dead bridge loads were determined, and prestressing design of the precast beam completed according to prestressing calculations. The loads which have been considered during the design of the bridge is given below.
1.Self weight of girder and deck
2.Asphalt weight
3.Curbs loads
4.Pedestrian railing loads
5.Guardrails loads
6.Side panel loads
7.H30-S24 Standart truck live load
8.Design lane live load
9.Pedesterian loads
10.Seismic loads
After prestressing calculations, 21 prestressing strands have been determined to be used in the precast beam. As prestressing stress may exceed the alowable stresses, the stresses have been computed for both support section and span section under the all vertical loads with condition both transfer and service stage. After the stresses have been compared with the allowable stresses which are defined in AASHTO LRFD 2017 specification, it has been realized that the tension stress in support section for transfer stage does not satisfy the requirements with the specification.  To reach the allowable stress, 4 number of strand have been debonded. After prestressing design, bending moment and shear strength have been calculated. As a result, tension and shear reinforcement have been determined. Thenafter, a computer model of the bridge was formed in the SAP2000 program, and the stiffnesses of the elastomeric bearings have been calculated to define in the software model. The model has been set with the frame elements. All the precast beam and slab have been defined with frame element. Elastomeric bearing has been defined as lineer links. The connection of the superstructure and substructure has been provided with fictive elements. All the vertical, horizontal and earthquake loads together with their combinations as per the related specifications have been introduced and structural analyses completed acordingly. After analyses completed, the design forces have been determined. Reponse modification factor has been taken 3 for longitudinal direction and 5 for transverse direction according to AASHTO LRFD 2017 specification. Structural design of reinforced concrete piers and pier caps has been carried out as per these analyses results. Finally, bending and shear reinforcement have been calculated for piers and pier cap.
In the third chapter, a general information was given for the nonlinear analysis, and plastic hinge height of the columns and moment-curvature relations were explained. Moment curvature analysis has been performed using XTRACT software program. Additionally, horizontal elastic design spectrums of  DD-1 and DD-2 earthquakes were given to be used for the nonlinear analysis.  The seismic coefficients of bridge are taken from Turkey Earthquake Maps according to chossen DD-1 and DD-2 earthquake level. Thenafter, plastic rotational limits of the structural elements were determined as per the May draft  prepared by KGM and Yüksel Proje for Highway and Railroad Bridge and Viaducts. According to this report, four performance levels are defined which are  immediate occupancy, limited damage, controlled damage and collapse prevention.
1.Immediate Occupancy Performance Level (KK): This level of performance corresponds to the situation where structural damage does not occur or the damage remains negligible in the bridge main carrier system elements. At this level of performance, the elements are expected to be linear elastic or very close to it.
2.Limited Damage Performance Level (SH): This performance level corresponds to the limited and easily repairable level of bridge main carrier system elements.
3.Controlled Damage Performance Level (KH): This level of performance corresponds to the level of controlled damage in the bridge main carrier system elements, which is not very heavy and often repairable.
4.Collapse Prevention Performance Level (GÖ): This level of performance corresponds to the pre-crash situation where severe damage occurs in the bridge bearing system elements. Partial or complete collapse of the bridge is prevented.
Finally, stages of the nonlinear static pushover analysis were presented.
In the fourth chapter, a nonlinear analysis of the structure was carried out, and its performance determined under DD-1 and DD-2 eartquakes. Before nonlinear analysis, plastic hinges have been defined at the end od the columns. In this context, static pushover and capacity curves have been obtained using the SAP2000 program. The calculated capacity curves together with both the horizontal earthquakes design spectrums have been examined together, and the performance point of the bridge was determined. Plastic hinges have not been observed as a consequence of static pushover analysis which has been performed until the amount of demand displacement. Therefore, elastic behavior has been observed under both the DD-1 and DD-2 earthquakes  conditions, and it has been determined that the bridge is at the  immediate occupancy performance level.
At the fifth chapter, the calculation results have been summarized and commented. The results are summarized below.
1.Total length of a two equal span bridge designed as per AASHTO LRFD 2017 specifications is 46 m and pier height 12 m. Central pier of the bridge is composed of 3 piers each 180 cm diameter. Each span is composed of 8 precast prestressed beams each with 23m length. Each beam rests on elastomeric bearings at both ends.
2.21 numbers of prestressing strands have been used in 23 m long precast beams. 4 number of strands have been debonded in support sections.
3.As per structural analyis of the system 37Ø32 mm  reinforcement in the vertical direction and Ø16 stirrups at 10 cm have been found for each pylon of the bridge piers.
4.As per structural analysis of the cross-beam of the bridge 30 numbers of 20 mm diameter reinforcing steel have been used in the longitudinal direction together with triple 12 mm diameter closed stirrups spaced at 10 cm apart.
5.For the nonlinear analysis of the structure, plastic joint length has been calculated and such joints has been formed at the upper and lower sections of columns.
6.At the end of the DD-2 earthquake performance analysis it is witnessed that the horizontal elastic design spectrum has cut the capacity curve of the structure at the elastic zone. As a result of this, it is seen that no plastic joint has been formed. It is witnessed that under DD-2 earthquake loading the behaviour of the structure is totally elastic and behaved in a Uninterrupted Service performance level.
7.At the end of the DD-1 earthquake performance analysis it is witnessed that the horizontal elastic design spectrum has cut the capacity curve of the structure at the elastic zone. As a result of this, it is seen that no plastic joint has been formed. The anlysis showed that under DD-1 earthquake loading the behaviour of the structure is totally elastic and behaved in a Uninterrupted Service performance level.
8.It has been acceptable to stay within Controlled Damage performance level for the DD1 earthquake according to Highway and Railway  Bridge and Viaducts Draft Report. For this reason, it has been understood that dimensions of the columns within the structure could be decreased to a certain extent.