Upper Structure of Precast Concretes Comparison: PC-I and PC-U in West Outer Ring Road

model with PC-U prestressed beam had smaller ratio than PC-I. The comparison of strand used in PC-U beams was more than PC-I with 42.22%. The maximum moment value was occurred in PC-I girder beam was 1541.979 Tons.meter and PC-U girder was 2252.599 Tons.meter. The strand requirements and cross area section was comparised too.


Introduction
The increase in the volume of motorized vehicles has an impact on traffic congestion and the road capacity is exceeded. Traffic congestion occurs because the vehicle speed is too slow and does not match the planned speed, causing heavy traffic [1]. The increase in the volume of motorized vehicles also causes congestion in West Surabaya. To reduce congestion in West Surabaya, the government built a flyover on the west outer ring road. The fly over structure is the same as the bridge structure, consisting of an upper and lower structure. The upper structure consists of a floor structure, girders and diaphragms [2]. The structure of flyover is same as the bridge. The Bridge is one of the infrastructure buildings that industrial, economic, and social growth of a region [3]. The bridge is structure that joints two or more points which are separated by rivers, valleys, and others [2]. Precast concrete elements, such as bridge girders, have been used successfully in bridge construction for many years. These elements have adapted to challenging and continuously evolving requirements related to serviceability and constructability [4]. A bridge structure is divided into two parts, upper structure and lower structure. The upper structure consists of pavement, traffic deck, diaphragm, and girder, the lower structure consists of abutment, pillar, bearing, and foundation. Bridge structure has variety of type, based on its material and system. This study aimed to compare PC-I Girder and PC-U Girder of Upper Structure. The PC-U girder is an attractive alternative to the I-girders [5].
There are many types of prestressed concrete girders including PC I Girder, PC U Girder, Box Girder and the Voided Slab. Each type has its own advantages and disadvantages [4]. Girder is the main beam on the bridge/fly over. The use of precast concrete as a girder has been used in many bridges because of its better quality and practical use. There are 2 precast concrete girder shapes, namely I shape (Precast Concrete I-PC-I) and U shape (Precast Concrete U-PC-U). The PC-I girder has a sleek design and is proven to be sturdy. The taller and slimmer the PC-I girder is, the more vulnerable it is against torsion. The development of the PC-U girder is attempted to overcome the occurrence of torsion. PC-U girder has an area of larger area than the PC-I girder, so that it affects the increase in the volume and weight of the superstructure. However, the PC-U girder can reach the maximum distance between the girders, almost 2 times longer than the PC-I girder, meaning that more girders are needed when using PC-I girders. In addition, the PC-U girder has a maximum span length that is 1.2 times shorter than the PC-I girder [6]. Upper Structure of West Outer Ring Road Flyover uses Precast I Section Girder. PC-I Girder has slim form and proved sturdy, therefore PC-I Girder is used until now. However, using PC-I Girder which has slim form and high caused torsion. Over time, reinforced concrete bridge structures, especially girders, were developed so that various models or girder forms emerged. PC-U Girder is one of girder form. Girder has function as a support for vehicle load which distributed to lower structure, such as abutment, pillar, bearing and foundation. The using of PC-U is still rarely found on precast concrete bridge system in Surabaya. PC-U has a larger cross section than PC-I. This has an impact on the overall weight of a precast reinforced concrete bridge structure. With different shape and area section both of PC-I and PC-U girder, the behavior of element also different. Beside, PC-U has longer maximum distance between girder than PC-I, PC-I Girder has maximum distance between girder 1,85 meters and PC-U 3,1 meters. The PC-I has a maximum span of 50 meters while the PC-U is only 40 meters. From this study, the result will be as reference in using PC-I and PC-U Girder of precast structure design.

Literature Review
Flyover is a structure which carries one road over the top of another road to manage the traffic. Flyover structure is planned with bridge code [7] and urban geometry road standart [8]. Several previous studies have compared the use of PC-I and PC-U girders. Among them Upper Structure of Precast Concretes Comparison: PC-I and PC-U in West Outer Ring Road are [3] which compares the use of PC-I and PC-U girders on the Wonogiri Gorge Bridge. The results showed that the number of PC-U girders needed was less than that of PC-I girders. In addition, the tendon, moment, and shear reinforcement in the PC-U Girder bridge is more than that of the PC-I Girder bridge. Another study, conducted by [6], compared the use of PC-I and PC-U girders on the Marthadinata Bogor Flyover. The results showed that the use of PC-I girders was 18% more cost-effective than PC-U girders. [9] also conducted research on the use of PC-I and PC-U girders on the Mahakan Samarinda IV Bridge. The results showed that the loss of prestressing force on the PC-I girder was 14% more than the PC-U girder. By considering the total value of prestressing loss, number of girders, girder height, and overturning forces that occur in PC-I and PC-U girders, the use of PC-U girders is considered much safer, economical and efficient. In 2019, [10] was compared PC-U type and PC-V type. The results showed that using PC-V type girder gains the benefit of efficiency in terms of both cost and time, this is showed by the percentage of production PC-V girder is 97% faster then PC-I girder. [11] compared PC-I and Box Girder due to stiffness and deflection, the result percentage of loss of prestressed PC-I was higher than box girder, while deflection of box girder was higher than PC-I. [12]was conducted research PC-U Girder due to vertical bearing capacity and damaged web can lead to failure structure, furthermore [13] analyze the PC I girder design used on the bridge, impact of load combination due to behavior. In 2018 [14] proposed PC-T girder which is optimized prestressing layout and reduce conventional reinforcement and combined with steel fibers. Two large scale spliced I-Girder specimens and CIP as part research program aim to evaluated the shear strength and behavior [15].
Based on the results of previous studies, there are many factors in determining the use of the two types of girders. In this study, a comparison of the use of PC-U and PC-I girder reviews all aspects reviewed by previous researchers by adding a review of their effect on pile requirements.

a. Design Criteria
Pre-stressed concrete is basically concrete in which internal stresses of a suitable magnitude. In reinforced concrete members, the pre-stress is commonly introduced by tensioning the steel reinforcement [16]. Prestressed concrete structures the approach to design takes the form of cost optimization problem because different materials are involved [17]. The function of prestressing is to place the concrete structure under compression in those regions where load causes tensile stress [18]. The proposed PCI-girder is selected from the manufacturer's brochure based on the span length. The length of the flyover span is 40m, so the height of the PC I girder is 210cm. The compressive strength of concrete, fc' = 50 MPa. Elastic modulus of concrete,= 4700 √ fc' = 338893,94 kg/cm², Poisson's number,υ = 0,20 , Shear modulus,G = Ec/ [2*(1 + υ)] = 13848 MPa , Coefficient of long expansion for concrete,α = 0,00001 / ºC , Distance between girders (beam spacing) = 150 cm.

b. Precast Concrete Analysis
There are two methods of prestressing, pre tension and post tension. Pre tension method is apply prestressed to steel strands before casting concrete, whereas post tension is apply prestress to steel tendons after casting concrete. Because the strength of concrete is very dependent on the level of tension or the magnitude of the prestressing force, there are two terms in prestressing, namely fully prestressed and partially prestressed. For fully prestressed concrete structural members, the structure is designed to prevent cracking at service loads, so the fully prestressed concrete structural components are determined to determine the tensile stress that occurs. In planning a prestressed concrete bridge structure, the loss of prestressed force must be considered, because the stress on the prestressed concrete tendon decreases continuously over time [19].
Loss of prestress is a reduction in the force that occurs on the tendon when it is loaded. Loss of prestress is divided to: 1. Short term loss of prestress. 2. Loss of prestress due to influence time.

Research Method
The method used in loading analysis and structural performance on the west outer ring road flyover with PC-I and PC-U beam girder reinforcement using SAP 2000 program. The research steps are: 1. Collection of literature studies and previous research. Literature review from books, building code, scholary articles, and any other sources relevant to this study. 2. Secondary data collection includes plan data, soil data and others.
There is two kinds of plan data, primary data (shop drawing) and secondary data (soil data).     Cross Section of West Outer Ring Road Flyover with PC-I Girder According Figure 2, cross section using PC-I Girder type H-210 can be seen that with a total width of 10.35 meters, 6 PC-I girders are needed, the distance each of girder is 1.5 meters. : The combination of earthquake loading where the importance of the bridge affects the live load factor EQ when the earthquake happened.

Prestress Analysis
Calculate initial condition of prestressed concrete (load transfer) due to material property. Furthermore, determine strand type aimed to obtain amount of tendon from initial condition, then loss prestressed is calculated. 6. Modelling using structural analysis Program In this step, modelling was used SAP 2000 program to determine the period of the vibrating structure and internal forces working on the structure. 7. Structural performance control. Structural performance control due to load combination, deflection, and momen ultimate.

Comparison Result
The comparison results on the PC-I girder and PC-U girder structures are obtained after controlling the two structures when given the same load so that the forces that occur are in the form of maximum moment, maximum shear and axial. 9. Conclusions.
The conclusions are the results of a comparison of the forces or reactions that occur in the structural elements, the behavior of PC-I and PC-U structural elements and the impact of using PC-I girder and PC-U Girder on the flyover.

Results and Discussions 3.1 Cross section area of the beam
There is any differences between PC-I Girder and PC-U Girder due to section area, the difference can be described in Figure 4 below.   Table 2. From the Table 2, it can be seen the value of area section PC-I (5,176 m 2 ) is larger than PC-U (5,100 m 2 ).

Prestressed Beam Reaction
Then, the next stage is to conduct internal force between PC-I and PC-U Girder which is used to compare Moment and Shear Forces both of PC-I and PC-U. Using SAP 2000 software, Moment and Shear Force are obtained in Table 3 as follows.

Loss of Prestressed
Loss of prestressing force is force reduction that occurs in the tendon when loading is carried out, it is necessary to analyze the loss of prestressing force. So in this study the loss of prestressing force on the PC-I Girder and PC-U Girder was compared. From the Table 4, it shows that loss of prestressed that occur in PC-U Girder is higher (percentage of loss of prestressed=24%) than PC-I ((percentage of loss of prestressed=21%).

Conclusion and Suggestion 4.1 Conclusion
Based on the analysis of the calculation results that have been carried out and using the SAP 2000 software, conclusions can be drawn including : 1. Due to calculation of floor slab reinforcement, the difference in the ratio of reinforcement in the flyover model using prestressed beams PC-I Girder and PC-U Girder with each ratio value for the support area is 0.00440 and the field area is 0.00387 for the model with using PC-I Girder. Meanwhile, for the model using PC-U Girder, the reinforcement ratio in the support area is 0.00412 and the field area is 0.00363. So that the ratio required for the floor slab with the flyover model using PC-I Girder prestressed beams is higher, this is caused the PC-I girder model is different from PC-U, in the PC-U model the area of the slab that is not supported is more visible. smaller than PC-I so that it affects the ratio of floor slab reinforcement. 2. Based on calculation of the area of the PC-I prestressed beam, an area of 5,100 m2 with 6 beams is obtained, while the PC-U prestressed beam has an area of 5,176 m2 with a total of 4 beams, so that the area of the flyover with the PC-U girder prestressed beam model 3.45% wider than PC-I. 3. The use of Strands on PC-I Girder beams requires as many as 60 Strands for 1 prestressed beam so that the bridge structure with PC-I Girder prestressed beams requires 360 strands while the beam PC-U Girder prestressing requires 128 for 1 beam so it requires 512 strands for a bridge structure with PC-U girder prestressing beams. So that the percentage ratio of 42.22% is Ton.m each caused by a combination of 1D Strong load. so that in the use of PC-U there is a difference of 0.53% greater than the pillars in the use of PC-I Girder. The maximum shear value for the flyover model using PC-I Girder prestressed beams is 6,3788 tons caused by the combination of Strength 5, while for the flyover model using PC-U girder the value is 4,394 Tons obtained from the 1D Strength combination. so that in the use of PC-I there is a ratio of 45.17% greater than the PC-U girder. 5. In the result loss of prestressed beam for PCI Girder, the prestressing force loss is 21% while for PC-U Girder by 24%. This result was caused PC-U Girder need more strand than PC-I Girder.

Suggestion
Due to better research result in further search, authors suggest the following: 1. Analysis of the calculation of prestressing beams, understanding and accuracy are needed in order to obtain more accurate results. 2. It is necessary to understand the SAP 2000 V14.2.5 auxiliary program. Especially when controlling the structure (behavior and internal forces) so that the resulting output is more accurate.