Hi Andy,
SketchUp's annotations and dimensions do not go well inside the model viewer of Trimble Connect. It is a known issue and is being looked into. In general it is recommended not to include native authoring tool specific information to the shared collaborating environment, like dimensions, annotations, Styles, watermarks, backgrounds etc.
Since your structural engineer is using the same authoring tool, Trimble Connect can simply act as a filesharing service and he can download and open the model in SketchUp locally.
If you do want a plain model, create a "Trimble Connect Scene" where all is set to be viewed with the 3D Viewer from Trimble Connect and than upload it, or select the file and choose 'Edit in SketchUp' to open the Web application and explore the model in SketchUp Style:)
------------------------------
Jack de Moel
------------------------------