heavy load; heavy weight
Literal physical heaviness, often used for cargo, luggage, or structural load.
The horse endured the heavy load and climbed the slope.
burden of responsibility; heavy duty
Figurative use for a weighty responsibility or demanding obligation.
He could no longer bear the burden of responsibility as president.
A heavy load is being applied to this bridge.
This pillar is designed to withstand a heavy load.
He bears the heavy burden of keeping the company alive.
負担 is the common, general word for a burden or strain (physical or mental), while 荷重 is rarer and stresses the sheer heaviness of a tangible load or duty.
重責 specifically means a heavy responsibility or important duty, whereas 荷重 can describe either a literal heavy weight or a figurative heavy duty.
Compound of 荷 (に, 'load, cargo') and 重 (おも, 'weight, heaviness'). The reading におも is a native Japanese compound.