Windows changed, cracks appeared. Lintel issue?

SouthLondonHusband

We had the window frames in an old bay window replaced in the summer (new ones pictured below, since been plastered over). Since then, cracks have appeared in the mortar on the right hand side of the brickwork surrounding the window (pictured below, crack at the top and middle). Should this be a simple external repointing to fix the cracks, or should we be worried about the structural integrity of the bay since the replacement? As pictured below, the installers added wooden frames and there are joists on the left and right that come down from the loft, but no main central lintel. 

stuart45

I don't think it's a lintel issue. The segmental arch takes the place of a lintel.
Brick piers don't have a lot of lateral strength, and rely on the weight above to keep them stable. The upper floor ones have a lot less weight on top, so movement is more likely. It often happens when windows are replaced. I've had to rebuild a few. 
It might be possible to grind out some of the joint in the arch and pump some grout in, and then repoint. It doesn't look to bad at the moment. The other cracks can be repointed.

Section62

stuart45 said:

I don't think it's a lintel issue. The segmental arch takes the place of a lintel.
Brick piers don't have a lot of lateral strength, and rely on the weight above to keep them stable. The upper floor ones have a lot less weight on top, so movement is more likely. It often happens when windows are replaced. I've had to rebuild a few. 
It might be possible to grind out some of the joint in the arch and pump some grout in, and then repoint. It doesn't look to bad at the moment. The other cracks can be repointed.

I wonder to what extent the arches are structural and how much just decorative.

For an arch to bear load the springings need to provide a reaction, the vertical arch load being translated into lateral loads on the supports.  As you point out, brick piers don't have much lateral strength, so an arch springing from the top of a pier typically needs a balancing force on the opposite side of the pier to stop the pier moving away from the arch.

I've not worked on an arrangement like this myself, so just hypothesising, but I'd not rule out the possibility the old frames were doing more work than was expected... even the possibility they were acting as ties keeping the piers in the right place?

Edit: also worth noting the small (bathroom?) window in the house next door has had some extensive work done to the surrounding brickwork - possibly the insertion of a lintel?

stuart45

They normally have timber lintels on the inside, which probably do most of the work. As you point out, an arch on it's own would tend to push out the piers, so they are partly decorative. With a 9 inch wall, a lintel on the back 4 inches can take enough of the load to free up the front which is often a camber or segmental arch.