Here you can find the frequently asked questions regarding assessing buildings using the Reference Approach.
11.1. What really determines the diaphragm capacity of floors and roofs? How much of an influence does the spanning direction have?
The diaphragm capacity of floors and roofs is primarily determined by the shear capacity of the load transferring
element. This is usually the sheet(roof boarding) attached to the beams/girders and purlins.
If the floor/roof sheet is orthotropic then the weaker stiffness direction governs the shear capacity of the sheet and
ultimately the roof. This is more important for planks than for plates. However, it is also important to look at the
connection between the walls and the floor/roof. In practice however, it is not common to look into this but evaluate
the diaphragm capacity based on the material of the sheeting.
11.2. How can I check that both leaves of a cavity wall will comply after application of a wall tie?
11.3. Can I use a reference building that has a lower PGA?
It is possible to use a reference building with a lower PGA however, a general rule of thumb is used to limit the
minimum PGA. A reference building with 20% lower PGA can be used as long as the deformations in the referenced element
are limited to 20% of the deformation limit criteria. Which leaves 80% reserve deformation capacity in the element
(mostly walls are considered).
11.4. Is it correct to compare buildings based on ‘Unity check’ of deformation?
The unity check ‘U.C.’ can stay in the report and UPR but be aware that a non-linear analysis is used to assess the
referenced buildings. Thus, a linear proportionality of the estimated deformation is not accurate. The U.C. should
simply be used to get an indication of the reserve capacity of the elements in the reference buildings and if the
plastic domain is reached.
11.5. What should be the bottom boundary condition of walls resting on timber floors for NLKA?
A flexible bottom boundary , condition 5, should be used.
11.6. Can a floor be divided into parts along the line where it is supported by a girder?
The dimensions of a floor that can be considered as a separate diaphragm area should essentially be the area bound by
walls (all edges supported on walls). However, in case where there is a joist supporting the floor, then it is
important to check if that joist can efficiently resist lateral loads thereby becoming the bounding edge of a
diaphragm area. In order to do this, the lateral load carrying capacity of that joist needs to be checked.
Three scenarios can be elaborated for this.
Joist is resting/supported by walls where at least the axis of one wall is aligned with the axis of the
joist (as shown in the figure below). This way the joist can make use of the lateral load carrying capacity of
the wall. As a result, the floor diaphragm area can be bound, on one side, by this Joist!
Joist is resting/supported by walls where none of the walls have their axis aligned with the axis of the
joist. In this case the floor diaphragm area cannot be bound by the joist!
Joist is supported on columns (a frame system). In this case the lateral stability of this frame needs to
be investigated and if it is believed that the frame has sufficient lateral load resisting capacity then the
floor diaphragm area can be bound by this Joist!
11.7. Are prefab dakplaten or ‘Unidek’ roof panels considered plates or planks?
Insulated prefab dakplaten or ‘Unidek’ roof panels have a capacity that is close to planks. However, since they are
usually anchored to the roof rafters (good connection), they are normally not strengthened. A wind bracing may be
suggested as a measure if considered necessary.
11.8. How can existing deformation of walls be considered in the assessment?
When assessing big deformations (settlements-rotations), you need to consider 4 aspects:
Loss of capacity: in-plane there is still friction and interlocking so not a big issue, check for out-of-plane.
Deformation OOP: which you can add to the NLKA
Pre-stressing because of the big differential settlements: maybe it is near to cracking or breaking.
Connection check: if connections are not in good state check them or propose measure connection.
Keep in mind that if the settlements are still on-going and not stable yet and strengthening measures are applied to
the parts that shows deformation then these locations will attract more forces → in this case add to the report that
it is suggested to monitor the settlements.
11.9. Can hollow core slabs (HCS) be treated as solid concrete slabs?
If the hollow core slab (HCS) does not have a structural top layer then it is recommended to consider it critical and
check using a reference building against the shear capacity of the HCS which is governed by the shear capacity of the
joints. However if a structural top layer is present, then the shear capacity of the top layer is used as the capacity
of the floor.
11.10. How to assess the out-of-plane capacity of ‘Klampmuur’ walls?
‘Klampmuur’, dutch for ‘clamped-wall’, is built by attaching a 50mm thick wall (bricks are oriented in their narrow
thickness) to the existing masonry clay walls. For out-of-plane assessment, the main wall can be assessed with the
extra mass of the additional clamped wall.
