A tubular support assembly, comprising: a spider configured to support a vertical tubular string received therethrough, wherein the tubular string is configured to be positioned at least partially within a vertical sub-sea riser; a rotary adapter bushing that supports the spider and transmits a vertical load applied to the spider to a floating drilling rig, wherein the rotary adapter bushing defines an inner diameter through which the vertical tubular string is received; and a load cell configured to measure a value for the vertical load, characterized in that the value for the vertical load includes a weight of the tubular string and a dynamic heave-induced load applied to the tubular string by a heave of the floating drilling rig; the inner diameter of the rotary adapter bushing defines a shoulder; the load cell comprises: a first ring providing a loading surface, wherein the spider is seated on the loading surface; a second ring separated axially apart from the first ring by a plurality of ribs, wherein the second ring is seated on the shoulder of the inner diameter of the rotary adapter bushing, such that the load cell is received into the inner diameter of the rotary adapter bushing, and wherein a distance between the first and second rings varies in response to the vertical load, which axially-compresses the load cell between the spider and the shoulder; and one or more strain gauges that provide a signal that varies based on the distance between the first and second rings. a spider configured to support a vertical tubular string received therethrough, wherein the tubular string is configured to be positioned at least partially within a vertical sub-sea riser; a rotary adapter bushing that supports the spider and transmits a vertical load applied to the spider to a floating drilling rig, wherein the rotary adapter bushing defines an inner diameter through which the vertical tubular string is received; and a load cell configured to measure a value for the vertical load, characterized in that the value for the vertical load includes a weight of the tubular string and a dynamic heave-induced load applied to the tubular string by a heave of the floating drilling rig; the inner diameter of the rotary adapter bushing defines a shoulder; the load cell comprises: a first ring providing a loading surface, wherein the spider is seated on the loading surface; a second ring separated axially apart from the first ring by a plurality of ribs, wherein the second ring is seated on the shoulder of the inner diameter of the rotary adapter bushing, such that the load cell is received into the inner diameter of the rotary adapter bushing, and wherein a distance between the first and second rings varies in response to the vertical load, which axially-compresses the load cell between the spider a first ring providing a loading surface, wherein the spider is seated on the loading surface; a second ring separated axially apart from the first ring by a plurality of ribs, wherein the second ring is seated on the shoulder of the inner diameter of the rotary adapter bushing, such that the load cell is received into the inner diameter of the rotary adapter bushing, and wherein a distance between the first and second rings varies in response to the vertical load, which axially-compresses the load cell between the spider and the shoulder; and one or more strain gauges that provide a signal that varies based on the distance between the first and second rings.