Handrail, guard or vehicle barrier post
A steel post cantilevered from its base, under the code loads for a handrail, a guard or a passenger vehicle barrier, by ASCE 7-22 4.5.1 and 4.5.3, AISC 360-22 Chapters E to H and AISC Design Guide 34 (2018). The result is the post in flexure, shear and compression, its deflection, and its base: a plate on cast-in rods, or a post on a channel stringer's flange. Use the steel stair for the rail and the infill of a stair guard.
Inputs of the handrail, guard or barrier post #
- System: handrail or guard, or vehicle barrier for passenger vehicles. Truck and bus garages go to the AASHTO bridge specification (4.5.3): not here.
- Post: round or rectangular HSS, pipe, or W-shape. Height from the base to the top rail; the length of rail this post carries, usually the post spacing; K in compression, 2.0 prefilled, as Example 10.1.7, because a continuous rail may brace it and that is your decision.
- Guard loads: 200 lb at the top, and 50 lb/ft along the rail, not together. The uniform load has three exceptions in 4.5.1.1: clear its box where one applies. Both are prefilled and may be raised; less than the code's is a failed check.
- Barrier loads: 6,000 lb, at a height from 18 to 27 in. above the floor, 27 in. prefilled because it gives the largest moment. Less, or outside the range, is a failed check.
- Downward load together with the horizontal: a single load in any direction cannot be both, but Example 10.1.7 keeps them together. It is prefilled, on the conservative side, and is yours to clear.
- Dead load: rail and infill, and the post's weight. It only adds axial load here.
- Deflection limit: height / 60, the guide's Table 3-6 (twice the height over 120, from the IBC's limit for flexible finishes), under the load without a factor. Enter 0 to skip, as usual for a barrier.
- Base, plate on rods: the plate and its steel, the weld all around, rods by count, spacing, diameter and grade, the embedment, f'c, the concrete thickness, whether it is cracked, and the distance to a near edge in each direction. Post-installed anchors are not modelled: the largest rod forces are reported to take to that calculation.
- Base, channel stringer: the channel and its steel, for Eq. 7-1.
Auto-design varies the post within its family (round or rectangular HSS, pipe, W-shape), lightest first. The plate, rods, loads and height are kept.
Checks performed #
| Check | Basis |
|---|---|
| Code loads | ASCE 7-22 4.5.1, 4.5.1.1, 4.5.3 |
| Post flexure | F2, F6, F7 or F8, about each axis because the load acts in any direction, Lb = the height, Cb = 1 |
| Post shear | G2, G4, G5, G6 |
| Post compression | E3, E7 at K × the height |
| Axial load and flexure | H1-1, about the weaker axis |
| Deflection | V a² (3h − a) / (6 E I), the lower I |
| Rods | ACI 318-19 17.6, 17.7, 17.8, in each direction. LRFD whichever method you use for the post, with 1.6 on the load, because Chapter 17 is strength design. The dead load is left out as it holds the rods down, and the rods share the moment elastically about the group's center, without bearing under the plate |
| Plate | F11 at the post's face on the tension-side rods; the width is the plate's or the post's plus a 45° spread each side, our reading: no guide states it for this detail |
| Weld | J2.4, as a line around the post, no directional increase; Table J2.4 minimum |
| Post on a channel flange | The guide's Eq. 7-1, Beff = N + 2(2.5)(k − tf/2 + bf), web as a rectangular bar, F11-1 |
Limitations of this calculation #
Not covered: rails and infill; post-installed anchors; posts core-drilled or in grout pockets, or side-mounted; bearing under the plate; a W-shape post's weld; the torsion in a stringer and its end connections; load sharing through the rail; truck and bus barriers. Eq. 7-1 is the guide's author's suggestion from experience and finite element analysis, for a post alone. ASTM E985 was withdrawn when the guide was written; where a jurisdiction asks for a test (E935), this does not replace it.
Verification examples #
Verification status: 23 values compared in 2 examples (2 published, 0 hand calculations from the cited equations): 23 within tolerance, 0 recorded deviations. Thin: only 2 published examples. Code basis: the provisions it uses were read in the target edition.
AISC Design Guide 34, Example 10.1.7, the guard post: required strengths and available flexure, shear and compression, LRFD and ASD; and Example 10.1.8, the post on a C12X20.7's flange. Run at Fy = 46 ksi, as the guide's, through the A500 Gr. B select: this library takes 50 ksi for Gr. C, by the 16th Ed. Manual.
By hand, no published example on disk: the barrier, the rods' forces, the plate, the weld and the deflection. The rods' limit states are the shared ACI Chapter 17 library, verified with the concrete anchor. A guard post anchorage example would be worth finding (NAAMM's Pipe Railing Manual, purchase).