One of many tricks of the timber framer’s trade, the timber frame corner joint with spline and a tenon, is a great solution to the problem of several timbers coming together at one point.
There are many instances in timber framing when multiple elements of the frame converge in close proximity to each other. In this case, the tie beam and wall girt both connect to the post at the same spot. In order not to take too much wood out of the corner joint, one elegant solution is to use a spline joint on one horizontal member. The spline is set at the bottom edge of the timber. Since the tenon on the adjacent timber is located high on the beam, there is no conflict between the two. And the spline joint adds an interesting element to the joinery of the frame.
This works well as a repair where the corner post cannot be moved. The spline can be inserted from the OUTSIDE of the post. allowing the beam to be put in, and the spline secures it.