RAM Concept analyzes the concrete floor using a linear elastic global analysis. All deflection contour plans are representative of the linear elastic analysis and the particular load combination’s std load factors. The load history deflection calculations perform detailed calculations on the cross sections including the effects of cracking, creep, shrinkage, tension stiffening, and load history and then uses the results to modify the element stiffness in the linear elastic global analysis to calculate deflection contours considering the various effects. Dynamic effects are not considered.

In order to calculate load history deflections the load history must first be specified by the user. This is done in the "Load History" criteria page.

Each load history step represents an applied load combination for a specified duration of time. Each load history step is solved in sequence, taking into consideration the effects from all previous load history steps. For instantaneous load steps the duration can be specified as zero. The specified sequence of load steps makes up the entire load history. The total age at the end of each load history step is reported as a read only value in the table.

In order to calculate load history results, span segments and design sections must be specified such that each finite element with significant stress is covered by the tributary of a design strip cross section or design section oriented appropriately for the element stress. For one-way slabs, this could be achieved by defining span segments in the spanning direction only. For two-way slabs, span segments should be specified in orthogonal directions to cover the entire slab. Since the load history deflection detailed calculations are carried out on the cross sections and subsequently used to adjust element stiffness, omission of span segments or design sections in highly stressed regions will result in an inaccurate and potentially unconservative prediction of deflections.

RAM Concept ’s load history deflection calculations do not directly consider the effects from specified patterns, from live load reduction, or from alternate load factors.

Since the load history calculations can be time consuming, they are performed separately from other calculations in RAM Concept . They are invoked using the Calc Load History Deflections () command. The button will only be active if load steps are specified in the Load History criteria page and if the current load history results are out of date.

Results

The results for each load history step are available in the load history folder on the report tree. The results stored on each load history step represent the state of the structure at the end of the load history step. Additional load history steps can be added at any desired interval in order to calculate results at any particular age of interest.

Normally vertical deflections will be the results of most interest on a load history layer, but there are several other plot quantities that may also be of interest. The following plot quantities are only available for plot on load history layers, from the Slab Value menu:

fa/fcr - represents the ratio of applied axial stress over the cracking stress (normally the modulus of rupture). The applied stress is the result of applied loads and induced strains, including the effects of the input shrinkage restraint %. Only values greater than 0 are plotted, and any value of 1 or greater represents an area that will be considered as cracked for the load history calculations.

fa/fcr (unrestrained) - represents fa/fcr but with the effects of shrinkage restraint % removed. These values are plotted for information only to help understand the effects of the shrinkage restraint % value input. These values are not used directly in the load history calculations.

I/Ig - represents the modified long-term load history stiffness over the gross stiffness. This includes the effects of cracking, tension stiffening, creep, shrinkage, and all other load history effects. This number is normally less than 1.0 due to cracking and creep but can also be greater than 1.0 due to shrinkage warping that can counteract applied loads. This value is plotted in a spanning direction, so x-axis direction will represent stiffness in an x-oriented span resulting from cross sections oriented in a perpendicular axis.