The direction of Forces isn't necessarily along the connecting element. If that happens depends a lot on the constraints between the different elements. For example see the following image:
In the left column is a "welded" structure, while on the right column is a pin jointed structure (a basic truss) if you like.
On the top there are the shapes ...
It depends on the type of the joint:
The smooth dowel is used in an "expansion/contraction joint" to allow for free (lateral) movement due to thermal expansion/contraction of the concrete on either side of the joint. A smooth dowel has less surface for bonding, and no rib (small deformation around the bar) to restrict the movement. Sometimes ...
The reason why forces are transmitted in arches is similar to the joint structure in the other question. Additionally there are the internal bending moments that also change the undeformed shape of the element (be it beam or arch).
arches build with stone
Although not in your original post, I will focus on the forces in stone arches. In order to understand ...
The arch works by being deformed and compressed under the vertical loads.
When it deforms it wants to settle down and its geometry changes trying to trace a shorter path. But that shorter path means it strains the material creating compression stress in the material of arch, being it pieces of rock or concrete or masonry or even bags of dirt.
That is the ...
Strickly to say, this can only occur for fluid materials or airflow. For which you shouldn't have any problem in understanding how the diverging occurs.
Diagrams below show how the force flow in a hollow triangle (left), a rigid body (middle), and the random flow of the fluid force. Note there is no surface pressure/force in the first and second cases.
Young's modulus $E$ times
the second moment of area $I$ of the cross section.
The caveat is that this formula is simple enough when you have a beam made from one material. In the case of composite beams (ie. reinforced) the treatment is a bit more involved.
In general $EI$ provides a measure of the resistance of the beam to bending, which accounts for the ...