Horizontal Thrust Roof

As the roof load pushes downward vertically the rafters tend to spread outward at their lower ends pushing against the walls of the house.

Horizontal thrust roof.

This horizontal outward thrust can be considerable. To resist thrust the irc calls for a structural ridge required for any roof with a pitch less than 3 12 or for each pair of rafters to be securely connected to each other by a continuous ceiling joist r802 3 2006 irc. Horizontal rafter thrust this thrust calculator gives rafter horizontal thrust at the plates l rafter span building width w load on rafter roof design load. This thrust may push out the wall if the truss is not allowed to slip or the wall is not stiff enough to offer resistance.

The pitch is the number of vertical inches that a roof descends over the span of 12 horizontal inches. This force is resisted by horizontal rafter ties or. The vertical loads applied to the scissors truss create a horizontal thrust at the bearing. 1 where l is the rafter length projected onto the horizontal plane d is the rafter tributory width and σ is the roof loading projected onto the horizontal plane.

To resist thrust the irc calls for a structural ridge required for any roof with a roof pitch less than 3 12 or for each pair of rafters to be securely connected to each other at the lower end of the rafter by a continuous joist. In a simple gable roof the rafter boards carry the live and dead loads that push both downward and outward against the top of the load bearing walls. This horizontal load or thrust can be considerable especially on a low pitched roof. This horizontal load or thrust can be considerable especially on a low pitched roof.

Rafter and collar tie tension equation. The use of projections onto the horizontal plane seems to be the most commonly used approach. This horizontal movement translates into a vertical deflection which is most visible at the ridgeline.