u/Fast-Butterscotch553

Hi, I am currently working on my bachelor's thesis and want to create a model of a real bridge structure using SOFiSTiK. The goal is to match the natural frequencies to the actual structure and later simulate a vehicle crossing.

I already have a question at a relatively early stage regarding the modelling of the cross-section.

Specifically, I have a superstructure with 3 precast elements that are not connected to each other (2 cm gap, see image). These are connected via coupling plates and an in-situ concrete supplement. My question concerns the connection with the in-situ concrete supplement.

Could you tell me how I need to proceed so that the in-situ concrete supplement extends across the entire cross-section, while also being monolithically connected to the precast elements? It is important to me that the in-situ concrete supplement and the precast elements are not only connected at a single point, as this would affect the stiffness of the system.

Thank you very much — if you didn't fully understand the question, feel free to ask again.

https://preview.redd.it/cjdv4uvbcn2h1.png?width=1841&format=png&auto=webp&s=de3320314ea059bba2fe25a0e9724b983fdb71fa

Hi everyone, I'm writing my bachelor's thesis and this is my first time working with SAP2000, so please bear with me.

The superstructure is 4.54 m wide and consists of three precast concrete girders placed side by side (see Image 1,2). In reality, these three girders are connected to each other via coupling plates and act as one monolithic cross-section. I modeled each girder as a separate frame element.

On the left side I modeled a concrete wall as a shell element. In the middle there are 3 piers, one per girder, so that I can properly connect each pier to its corresponding girder.

When I run the modal analysis and inspect the mode shapes, the three frame elements deform completely independently from each other (see Image 3). They behave as if they are not connected at all, even though in reality they form one stiff cross-section. This independent behavior only occurs during torsional modes (image 3). For bending modes, the three girders deform together as expected (image 4)

Is there a reliable way in SAP2000 to couple three parallel frame elements so they deform together as one composite cross-section? The connection in reality is along the full length (via coupling plates), not just at discrete points.

Any help is appreciated, thanks in advance!